The town of Black Jack, Missouri, got its name from the variety of oak tree that once grew nearby. "Those stately trees represent who and what we are today, a proud city with strong roots, providing the safety and respite of community," its promotional literature explains. It is the kind of place where family is valued just as long as the family in question meets certain criteria. Olivia Shelltrack and Fondray Loving's family, it seems, do not.

The couple could face fines of US$500 a day, and Black Jack is already facing the unwelcome glare of national attention, as a result of a local regulation that bans unmarried couples with more than one child from occupying homes there.

"The character and stability of a city is not an accident, it is the result of years of hard work by the residents," Norman McCourt, the mayor of Black Jack, said in a statement after the city council rejected a proposal to abolish the regulation. Mr Loving and Ms Shelltrack now plan to file a lawsuit with the help of the American Civil Liberties Union, while the US department of housing, in Washington, has launched an investigation to determine whether Black Jack's ban is illegal.

Loving, 33, and Shelltrack, 31, have lived together for 13 years. They have two children and also live with Shelltrack's daughter, who calls Loving her father. They bought their Black Jack home earlier this year.

"We're just like anybody else," Shelltrack said. "It's not like we're purple with polka dots or something. I just really feel like this shouldn't be anybody's business."

The couple were not opposed to getting married, she said, but wanted to wait until they could afford a "nice big wedding... I don't think a piece of paper is going to validate our relationship, though. We love each other, and our kids are happy, healthy individuals. You can't define family."

Other American towns have regulations similar to Black Jack's, which technically bars any group of more than three people from living together unless related by "blood, marriage or adoption".

Generally, such rules are intended to stop rowdy college fraternity houses from being established on residential streets. But in a country increasingly divided on issues of social morality, housing regulations represent an easy way for towns to try to give their definitions of acceptable lifestyles the force of law.

In an earlier dispute, in 1999, McCourt wrote that city officials "do not believe that an unmarried couple having children, residing in our community, is an appropriate standard that they wish to approve." The family in that case broke the restriction because they had triplets.

Black Jack has backtracked on the mayor's earlier warning that Loving and Shelltrack might be evicted, but if it takes them to municipal court and wins it could fine them up to US$500 a day. Sheldon Stock, the town's special counsel, said a 1977 Supreme Court judgment had affirmed the view that a city could uphold traditional family values by limiting the number of unrelated people who share a home.

"I find it curious at best that housing laws are being used to define the relationships that count," said Frank Alexander of Emory University law school in Georgia, who has researched the phenomenon. "It seems a dangerous way to do indirectly what we may not be willing to confront directly, which is social control over the definition of family." Rules were being used increasingly, he said, to target immigrant communities "where extended familial relationships are common."

Michael Watson, a former marine who lives in Black Jack, has been taking a special interest in the case, since he too shares a home with his girlfriend and their children. He told the St Louis Post-Dispatch they had contemplated getting married, but were unwilling. "If I do get married, am I getting married out of super love, or am I getting married because Black Jack says I have to?"

Source: China Daily