Simply put, the town passed a law that any group of 3 or more people living together has to show ID for every resident, that unmarried couples (no matter how long together or how stable) cannot live there. This is a St. Louis middle-class suburb, according to the story. Unmarried families can be fined $500/day, the ACLU has taken the case on, the Black Jack City Council rejected a measure to change the law.
http://seattletimes.nwsource.com/html/nationworld/2003012539_blackjack23.html (clip)
The debate over how to define "family" has become increasingly heated after decades of changing social norms. And a growing number of urban and suburban communities are turning to housing and zoning laws to say what is — and isn't — a family, said Frank Alexander, interim dean of Emory University's School of Law in Atlanta.
"It's a not-so-veiled attempt to control who lives down the street and legislate relationships," said Alexander, who teaches a course on how housing laws define America's families. Black Jack Mayor Norman McCourt noted that no federal or Missouri law bars housing discrimination based on marital status. Missouri does not recognize common-law marriage.
Advocates say communities are just defending local standards. "They have the right to protect and restore a marriage-based moral order," said Robert Knight, director of the Culture and Family Institute at Concerned Women for America, a public-policy organization based in Washington...
(more at link)