The suit, filed on their behalf by the American Civil Liberties Union on Thursday, claimed that the town of Black Jack's housing law violates the state and US constitutions, as well as the Federal Fair Housing Act. It seeks unspecified damages.

The ordinance prohibits more than three people from living together unless they are related by "blood, marriage or adoption."

The ACLU said Foundray Loving, Olivia Shelltrack and their school-age children are facing fines of up to $500 per week for living in their five-bedroom home in the suburb of 6,800 because Loving is not the biological father of Shelltrack's oldest child, and the couple are not married.

"The government has no business saying two consenting adults cannot live with their own children," said Tony Rothert, legal director for the ACLU of Eastern Missouri.

City attorney Sheldon Stock declined comment. Mayor Norman McCourt did not return a phone call seeking comment. McCourt has previously said the ordinance was intended to prevent crowding and has nothing to do with morality.

The city council voted to keep the ordinance earlier this year.

Last month, a North Carolina judge struck down the state's 201-year-old law barring unmarried couples from living together, calling the law unconstitutional.

The ACLU says Florida, Michigan, Mississippi, North Dakota, Virginia and West Virginia also have laws that prohibit cohabitation. Missouri does not have such a law.