ALLENTOWN — A judge's decision out of Missouri last week means that federal courts are now split on the question of whether cities and towns may take steps to curb illegal immigration.

Anti-illegal immigration activists hailed the ruling by U.S. District Judge E. Richard Webber as giving a green light to municipalities nationwide to enact laws targeting illegal immigrants.

Opponents of local efforts say the issue is far from settled, noting that in a nearly identical case, a federal judge in Pennsylvania forbade the city of Hazleton from cracking down on illegal immigrants.

"This is a landscape characterized by significant legal uncertainty and these questions are going to glide their way up through courts," said Peter Spiro, who teaches immigration law at Temple University. "It certainly won't be the last word."

In the Missouri case, Webber upheld an ordinance in the St. Louis suburb of Valley Park that penalizes businesses that hire illegal immigrants. The judge rejected the American Civil Liberties Union's argument that the law discriminates against Hispanics and tramples on the federal government's exclusive power to regulate immigration.

The ordinance "is not pre-empted by federal law, to the contrary, federal law specifically permits such licensing laws as the one at issue," Webber wrote.

Webber's colleague in Pennsylvania came to a radically different conclusion last summer, striking down the Hazleton law as unconstitutional and saying the city had no business taking on what he called a federal responsibility.

Hazleton's measure, approved in 2006 and challenged by the ACLU, would have denied business permits to companies that employ illegal immigrants, fined landlords who rent to them and required tenants to register and pay for a rental permit.

Inspired by the Hazleton crackdown, dozens of local governments, including Valley Park, passed similar measures to curtail illegal immigration.