State law allows towns to enforce local laws giving police the authority to arrest anyone who swears at another person in a public place. Still, the U.S. Constitution’s First Amendment free-speech clause may be the ultimate trump card — if anyone felt like fighting a $20 ticket.

The Associated Press reported that “Mathew Segal, legal director of the American Civil Liberties Union of Massachusetts, said the U.S. Supreme Court has ruled that the government cannot prohibit public speech just because it contains profanity,”

In the 1974 Lewis v. City of New Orleans decision, America’s highest court reversed a lower court’s ruling that made it unlawful “to curse or revile or to use obscene or opprobrious language toward or with reference to” a police officer on duty. The ordinance was “susceptible of application to protected speech,” the court ruled, “and therefore is overbroad in violation of the First and Fourteenth Amendments and facially invalid.”