The state Senate of North Dakota had voted to keep a 113-year-old law that makes it a crime for unmarried couples to live together.

Efforts by the Democrats to repeal the law, which says a man and woman may not live together "openly and notoriously" as if they were married, was defeated in a party-line vote 26 to 21 last Tuesday.

The law, which has been on the books since 1890, carries a maximum 30 days in jail and a US$1,000 fine. The offence is also listed among other sex crimes including rape and incest.

Advocates of repealing the law are concerned that such laws intrude into citizens' private lives and are impossible to enforce or would require unorthodox police work.

"You're going to have to hire the sex police to get the pictures," said state Senator Linda Christenson, a Democrat. "This is such an intrusion into the privacy of people's relationships and living agreements."

Proponents however stand by their morals.

"It stands as a reminder that there is right, and there is wrong," said state Senator John Andrist, a Republican.

"Just because something can't be enforced, I don't think it necessarily means that we should feel compelled to take a position to take it off the books."

Republican Margaret Sitte said unmarried couples living together erodes the institution of marriage and hurts children and families. Such couples are more inclined to domestic violence and more likely to end up in divorce court if they do eventually wed.

"State law should not follow the pendulum of trends, but should set a standard for what is best for children, for men and women, and for society's best interest," she added.

2000 census data show that North Dakota has more than 11,000 unmarried couples living together, although the figure includes gay and lesbian couples. The law however refers only to one person living with another of the opposite sex.