Latino activists asked a federal judge Tuesday to block a voter-approved ordinance that prohibits landlords from renting apartments to most illegal immigrants in the Dallas suburb of Farmers Branch.

The Mexican American Legal Defense and Educational Fund, which has already sued the city, requested the temporary restraining order in U.S. District Court.

The ordinance, scheduled to take effect next Tuesday, requires apartment managers to verify that renters are U.S. citizens or legal immigrants before leasing to them, with some exceptions. Violators face fines of up to $500.

City council members first approved the ban in November without discussion, then revised it in January to include exemptions for minors, seniors and some mixed-status families. On Saturday, residents voted to approve the ban with 68 percent of voters in favor.

Councilman Tim O'Hare, the ordinance's lead proponent, contends the city's economy and quality of life will improve if illegal immigrants are kept out.

Farmers Branch already faces four lawsuits brought by civil rights groups, residents, property owners and businesses, who say the ordinance discriminates and puts landlords in the precarious position of acting as federal immigration officers. Their attorneys argue the ordinance attempts to regulate immigration, a duty that is exclusively the federal government's.

Nationwide, more than 90 local governments have proposed, passed or rejected laws prohibiting landlords from leasing to illegal immigrants, penalizing businesses that employ them or training police to enforce immigration laws.