The U.S. Constitution and a Colorado equal-rights amendment means cities cannot ban women from going topless in public, according to an activist group called "Free the Nipple."
Free the Nipple filed the lawsuit in federal court in Denver on Tuesday against the city of Fort Collins, Colorado, claiming also that the city's public nudity ordinance also chills free speech.
The equal-rights claim, which is also based on the 14th Amendment to the federal Constitution, says the anti-nudity ordinance discriminates against females because it bans women and girls from stripping to the waist while allowing males.
"It's a petty and sexist ordinance that shouldn't have gone this far in the first place," co-plaintiff Brittiany Hoagland told USA Today in a telephone interview.
Fort Collins had resisted a campaign to repeal the law, which Ms. Hoagland said left her and fellow activist Samantha Six with no choice but to sue.
Fort Collins Mayor Wade Troxell told the paper that while he cannot comment on pending lawsuits, the two women seem set on trying the case "in the press."
USA Today reported that city lawyers had not been served with the suit officially Tuesday afternoon, but were familiar with it because it had been posted online.
"I think the City Council thoughtfully addressed the topic ... there is strong support in the community for where we are at this time," the mayor said.