The Mann Act and Caminetti v. United States: Policing Unmarried Couples

What was the Mann Act of 1910?

The Mann Act was a federal law of June 25, 1910, officially titled the White-Slave Traffic Act, that made it a crime to transport women across state or national borders for prostitution or other immoral purposes. Its section 8 provided that it would be known by that name, and it was printed at 36 Statutes at Large 825 ^[1]. Congress passed it and President William Howard Taft signed it in 1910; it is named after its sponsor, Republican Representative James Robert Mann of Illinois ^[3][4].

The law grew out of a national alarm about "white slavery," the forced prostitution of women and girls. According to the Associated Press, it followed a congressionally appointed commission of 1907 that studied immigrant sex workers, a body which held that a girl would enter prostitution only if drugged or held captive ^[3]. Congress based the law on its power to regulate interstate and foreign commerce, a basis the Supreme Court upheld in 1917 ^[1].

The key phrase was broad. The original act punished anyone who knowingly transported any woman or girl across such lines "for the purpose of prostitution or debauchery, or for any other immoral purpose" ^[3]. The words "any other immoral purpose" were the opening through which the law would later reach couples who were neither buying nor selling sex.

Timeline

1. 1910June 25: the White-Slave Traffic Act, sponsored by Rep. James R. Mann of Illinois, becomes law.
2. 1913Boxer Jack Johnson is convicted by an all-white jury for traveling with his white girlfriend; he serves 10 months.
3. 1917January 15: Caminetti v. United States holds that "immoral purpose" covers taking a woman across state lines to be a mistress.
4. 1946November 18: Cleveland v. United States applies the Act to fundamentalist Mormons who transported plural wives.
5. 1986Congress makes the law gender-neutral and replaces "debauchery" and "immoral purpose" with criminal sexual activity.
6. 2015May 29: the current text of 18 U.S.C. § 2421 is enacted by Public Law 114-22.
7. 2018President Donald Trump posthumously pardons Jack Johnson.
8. 2025October 3: Sean Combs is sentenced to 50 months on two Mann Act counts of transportation to engage in prostitution.

What happened in Caminetti v. United States?

Caminetti v. United States was a 1917 Supreme Court decision holding that the Mann Act applied to men who took women across state lines to be their mistresses, even with no commercial element. The case combined three prosecutions ^[1]. F. Drew Caminetti and Maury I. Diggs had been indicted in May 1913 in the Northern District of California for taking two women from Sacramento, California, to Reno, Nevada; a third defendant, L. T. Hays, had taken an unmarried woman under 18 from Oklahoma City to Wichita, Kansas ^[1].

All three were convicted. Caminetti was found guilty on one count and sentenced to 18 months in prison and a $1,500 fine; Diggs was convicted on four counts, two of them concerning the same trip to Reno, and received two years and a $2,000 fine; Hays was sentenced to 18 months ^[1]. In Caminetti's case, the indictment charged that the purpose of the journey was that the woman should become his mistress and concubine ^[1].

The Supreme Court heard the cases together on November 13 and 14, 1916, and decided them on January 15, 1917, in an opinion by Justice William R. Day ^[1]. Justice James McReynolds took no part, and three justices dissented, so the convictions were affirmed by five votes to three ^[1].

Why did the Court read "immoral purpose" so broadly?

The Court read "immoral purpose" broadly because it held that the words of the statute were plain and had to be enforced as written. In its view, transporting a woman so that she would become a mistress or concubine was plainly an immoral purpose within the meaning of the Act, whether or not anyone expected to be paid ^[1]. Where the language of a law is clear, the majority reasoned, neither its title nor a committee report can change the plain import of its words ^[1].

The majority rejected the argument that Congress had meant to reach only commercialized vice, the organized trade in prostitution ^[1]. It also upheld the Act as a valid exercise of the commerce power, applied to the movement of persons across state lines ^[1]. The rest of the opinion dealt with trial questions, such as whether the jury could draw inferences from a defendant's partial silence, and decided them for the government ^[1].

The Court did not ignore the consequences. It acknowledged that its reading opened the door to blackmail on a large scale, since anyone who traveled with a partner could be threatened with federal prosecution, but it held that this possibility was no reason to refuse to apply the statute as Congress had written it ^[1]. The decision thus turned a law against forced prostitution into a federal rule on the travel of unmarried couples, at least when the trip had a sexual purpose.

What did the dissenting justices argue?

The dissenting justices argued that Congress had aimed only at commercialized vice and that the Court's literal reading distorted the law. Justice Joseph McKenna, joined by Chief Justice Edward D. White and Justice John H. Clarke, pointed to the Act's own title and to the House committee report ^[1]. For McKenna, the designation "white slave traffic" had "the sufficiency of an axiom," leaving no doubt about what Congress meant to prohibit ^[1].

The House report, he noted, stated that the bill did not attempt to regulate voluntary prostitution, let alone private relationships without any payment ^[1]. Reading the general words "any other immoral purpose" without regard to that context, he argued, extended the Act far beyond its subject. He also warned that blackmailers of both sexes had already arisen, using the threat of prosecution under the broad construction as leverage, and concluded that the result was grave ^[1].

The dissent did not prevail, but its argument did not disappear. Three decades later, in Cleveland v. United States (1946), Justice Frank Murphy dissented and urged the Court to overrule Caminetti, and Justice Wiley Rutledge, while concurring in the result, questioned whether Caminetti had been correctly decided ^[5]. The debate over literal and purposive readings of "immoral purpose" ran through the Act's history until Congress rewrote it.

How was the Mann Act used against unmarried couples?

After Caminetti, the Mann Act could be used against any man who crossed a state line with a woman for a sexual relationship outside marriage, and its most famous early target shows how selectively it could be applied. Jack Johnson, the first Black boxer to win the world heavyweight title, was convicted in 1913 by an all-white jury for traveling with his white girlfriend, and he served 10 months in prison ^[3]. President Donald Trump granted him a posthumous pardon in 2018, which cited the racially motivated nature of the prosecution, according to the AP ^[3]. The broader use of morals laws against interracial couples is examined in Pace v. Alabama and interracial fornication laws.

The Court continued to apply Caminetti for decades. In Cleveland v. United States, decided on November 18, 1946, it upheld the convictions of members of a Mormon fundamentalist sect who had transported plural wives across state lines, holding that polygamy fell within "any other immoral purpose" ^[5]. Justice William O. Douglas wrote that the Act was primarily aimed at commercialized sex but was not restricted to that end, and he noted that Caminetti had stood for almost thirty years ^[5].

There were limits. In Mortensen v. United States (1944), as summarized in Cleveland, the Court asked whether interstate travel was a calculated means of carrying out sexual immorality, and the Cleveland Court applied that test by asking whether the unlawful purpose was the dominant motive of the trip ^[5]. A couple's ordinary journey was therefore not automatically a federal crime; what mattered was the purpose of the transportation, which, as Douglas put it, is what guilt turns on rather than its accomplishment ^[5].

What does the Mann Act say today?

Today the Mann Act no longer mentions immoral purposes: 18 U.S.C. § 2421 punishes knowingly transporting any individual across state or national lines with intent that the person engage in prostitution or in any sexual activity for which any person can be charged with a criminal offense, with up to ten years in prison ^[2]. The change came in stages. Amendments in 1978 and 1994 addressed the sexual exploitation of children, and the 1986 revision made the law gender-neutral and replaced "debauchery" and "immoral purpose" with the reference to criminal sexual activity ^[3][4].

The statute's form has also changed. The Act was codified in 1948 as section 2421 of title 18, amended again in 1998, and replaced by a new section 2421 enacted by Public Law 114-22 on May 29, 2015, whose text also allows a state attorney general to request that state or local prosecutors be cross-designated to bring Mann Act cases ^[2]. Britannica's summary of the modern law emphasizes the transportation of minors, and the AP notes that many recent prosecutions involve people accused of taking children across state lines for sexual purposes ^[3][4].

Because the current text depends on whether the sexual activity is itself a crime, a trip by two consenting adults who are not married falls outside its purpose in practice; private consensual conduct between adults has been constitutionally protected since Lawrence v. Texas (2003), as explained in how Lawrence v. Texas undermined fornication laws. The law remains in active use for prostitution cases. In July 2025, the music executive Sean Combs was convicted on two counts of transportation to engage in prostitution while being acquitted of sex trafficking and racketeering, and on October 3, 2025, Judge Arun Subramanian sentenced him to 50 months in prison and a $500,000 fine ^[6].

Combs appealed. A three-judge panel of the U.S. Court of Appeals for the Second Circuit heard two hours of argument on April 9, 2026, and did not rule from the bench ^[7]. No decision on that appeal was found for this article as of October 28, 2026, so the outcome remains to be confirmed. The wider history of the state laws that once punished the same conduct is traced in a history of fornication laws.

Frequently asked questions

Is the Mann Act still in force?

Yes. Its core provision is 18 U.S.C. § 2421, which punishes transporting any person across state or national lines for prostitution or for any sexual activity that is a criminal offense, with up to ten years in prison. The "immoral purpose" wording that Caminetti interpreted was removed in 1986.

Who were Caminetti and Diggs?

F. Drew Caminetti and Maury I. Diggs were two men indicted in May 1913 in the Northern District of California for taking two women from Sacramento to Reno. Caminetti received 18 months and a $1,500 fine, Diggs two years and a $2,000 fine. Their appeals produced the Supreme Court's 1917 ruling.

Why did Justice McKenna dissent?

Justice McKenna believed Congress had targeted only commercialized vice. He relied on the Act's official title, the White Slave Traffic Act, and on a House report saying the bill did not attempt to regulate voluntary prostitution. He also warned that the broad reading was already being exploited by blackmailers.

Was Jack Johnson convicted under the Mann Act?

Yes. The heavyweight champion Jack Johnson was convicted in 1913 by an all-white jury for traveling with his white girlfriend, and he served 10 months in prison. President Donald Trump pardoned him posthumously in 2018.

Is it illegal to cross state lines with a girlfriend or boyfriend?

No. Since 1986 the Mann Act covers transport for prostitution or for sexual activity that is itself a criminal offense, not a consensual relationship between adults. Between Caminetti (1917) and that revision, however, taking a partner across state lines for a sexual relationship outside marriage could be prosecuted as an "immoral purpose."

Why was it called the White Slave Traffic Act?

The name reflected the fear of "white slavery," the forced prostitution of women and girls, that drove its passage in 1910. Section 8 of the Act provided that it would be known as the White Slave Traffic Act. The dissenters in Caminetti argued that this title proved Congress meant only commercial vice.

What was Sean Combs convicted of under the Mann Act?

Sean Combs was convicted in July 2025 on two counts of transportation to engage in prostitution under the Mann Act, and acquitted of sex trafficking and racketeering. On October 3, 2025, he was sentenced to 50 months in prison and a $500,000 fine. His appeal was argued before the Second Circuit on April 9, 2026.