Dallas ? Two civil rights groups filed a lawsuit Tuesday challenging a new law in a Dallas suburb that outlaws renting apartments to illegal immigrants, alleging the ordinance violates federal law and forces landlords to act as immigration officers.

The American Civil Liberties Union and the Mexican American Legal Defense and Education Fund filed the suit on behalf of residents and landlords in Farmers Branch, just north of Dallas. It is the third lawsuit brought against the city since the ordinance passed in November.

The lawsuit claims the measure, scheduled to take effect Jan. 12, is so poorly drafted that it excludes even legal immigrants from renting.

“Immigration enforcement must be left to the federal government, not each local municipality,” said Lisa Graybill, legal director of the ACLU of Texas. “Otherwise Texas will end up with a patchwork system that is impractical and unenforceable.”