If a married woman has sex with a man other than her husband, whether he's married or not, both are guilty of adultery under Minnesota law.

It's a law that dates back to Minnesota's territorial days, when many early states were adding similar language to their statute books. But over the years, states have been gradually repealing laws criminalizing adultery, arguing they are rarely enforced and a relic of more puritanical times. One state legislator wants Minnesota to do the same.

"When I read it I couldn't believe it," said Rep. Kelly Moller, DFL-Shoreview, a prosecutor who has introduced a bill to repeal the language entirely. "It's not something that's prosecuted anymore, but there's so much sexism that's built into this system, I thought, let's just get it off the books."

The way the Minnesota law is written, adultery is a crime usually for a woman and only sometimes for a man. The law doesn't address when a married man sleeps with a single woman, and it says a man has a legal defense if he didn't know the woman was married. Adultery is punishable by a fine of up to $3,000 and a year in prison.

The law managed to stay on the books over the years despite a revamp of Minnesota's criminal codes in the 1960s. At least 18 other states also still make sexual acts a crime if at least one of the partners is married to someone else.

Even though the laws are not enforced, adultery statutes stayed on the books in many states over the years because some lawmakers felt they encouraged good behavior. Some believed that eliminating the laws would increase acts of adultery.

But in Minnesota, the law has no practical effect. Minnesota is a no-fault divorce state, meaning that adultery can't be used as legal grounds for a divorce or used in custody or property battles.

The bill was heard in a late-night House public safety committee meeting this week, and most legislators were surprised the law was still on the books.

"As a woman that's married, I'm highly offended that my husband could do things a lot differently than me," said Rep. Heather Edelson, DFL-Edina. "You just think back on when this law was created, how different the conversation was to today."

Rep. John Lesch, DFL-St. Paul, pointed out that state law also criminalizes "fornication," which is defined as when "any man and single woman have sexual intercourse with each other." Under law, that's technically a misdemeanor, even though it's not enforced.

"Let's add that one, too," Lesch said about eliminating outdated laws.

The bill passed out of the committee on a voice vote with little debate.

"This should be an interesting floor debate," said Rep. Carlos Mariani, chairman of the committee.

Briana Bierschbach • 651-925-5042

Twitter: @bbierschbach