IOWA CITY (AP) - The Iowa Civil Liberties Union is asking the U.S. Supreme Court to overturn an Iowa law requiring certain sex offenders to live at least 2,000-feet from a school or day care facility.

The group filed a petition with the high court in its ongoing effort to have the law, one of the nation's strictest for governing where sex offenders convicted of abusing minors can live, declared unconstitutional.

"This law is not only an enforcement nightmare, but it is also breaking up families, separating parents from their children, causing homelessness and - unless changes are made - will likely cost taxpayers of this state millions," said Ben Stone, the organization's executive director.

"Our jails and prisons likely are going to be filled with law-abiding citizens who served their sentences years ago, but who will be incarcerated again simply because they cannot find a place to live under this law," he said.

The petition, filed Thursday, is the first step in the process of convincing the Supreme Court to consider the case. The Iowa Attorney General will file a response before the court decides by the end of the year whether to hear the case.

The petition is the latest attempt by the ICLU to have the law struck down.

The Iowa Legislature passed the measure in 2002 and since then more than a dozen states have adopted similar restrictions.

That same year, the ICLU, on behalf of more than a dozen convicted sex offenders, filed a class action lawsuit. Attorneys argued that the law infringed on constitutional rights, made housing difficult to find in many urban areas and would have the effect of creating penal colonies.

U.S. District Judge Robert Pratt agreed and issued an injunction barring enforcement pending appeals.

But earlier this year, Pratt's ruling was overturned by the U.S. 8th Circuit Court of Appeals, in St. Louis. A three-judge panel concluded that any trampling of constitutional rights caused by the law was tailored to serve a compelling interest, specifically the health and safety of all citizens.

The ICLU asked to have the ruling reviewed by the full court, but the request was denied.

In its petition to the U.S. Supreme Court, the ICLU argues that the Iowa law should be reviewed promptly because similar laws are being adopted in cities, counties and states across the nation.

This week, the eastern-Iowa town of Ely, which has no school or day care centers, passed an ordinance banning sex offenders from living in an area that covers most of the town.

Another challenge is enforcement. Prosecutors and law enforcement officials across the state have complained about the work involved in identifying offenders living in restricted areas and keeping pace with ever changing locations of day care centers.

Douglas Berman, a law professor at Ohio State University who specializes in sex offender law, said there are good reasons for the Supreme Court to take up the challenge.

"This is the kind of issue the court is likely to recognize will come up again and again," said Berman. "The question is whether the court thinks it's the right time. The only problem is the issue has not been as developed in other courts as it has in the Iowa case."