State officials are seeking to curb illegal immigration by choking the supply of jobs with the law, which threatens to pull the business license of any employer that knowingly hires an illegal immigrant.

Arizona makes for a striking laboratory. Its estimated population of 500,000 illegal immigrants is among the highest and fastest growing in the country, and illegal workers make up an estimated nine percent to 12 percent of the work force, mostly in low-skill jobs in the service, construction and landscaping industries, according to research at Arizona State University.

Legal challenges to the law were filed by business and immigrant rights groups, asserting that the law would usurp federal authority, lead to ethnic profiling and hinge on sometimes inaccurate government records. Businesses and immigration groups say they have already tallied some of the effects of the law.

Advocates for immigrants contend that, at a minimum, hundreds of people unauthorized to work have left the state or been fired. Some school districts have at least partly attributed enrollment drops to the law. Though the housing slump and seasonal economic factors make it difficult to pin down how much is attributable to the new law, illegal workers say employers are checking papers and are less inclined to hire them.

?EUR??,,????'??They started asking everybody for papers one day, and those like me that didn?EUR??,,????'???t have them were fired,?EUR??,,????'?? said Luis Baltazar, a Mexican immigrant who worked for a paving company until a few weeks ago and was soliciting work at a day labor hiring hall.

Another immigrant, Jose Segovia, said work had plummeted in the past few weeks, more so than in the four previous Decembers he spent in Phoenix. ?EUR??,,????'??Some of my friends went back to Mexico,?EUR??,,????'?? Segovia said, ?EUR??,,????'??and I am thinking of going, too, if it doesn?EUR??,,????'???t get better here.?EUR??,,????'??

The law calls for suspending a business license for at least 10 days on the first offense and revoking it for a second one, effectively shutting down the business. Several states call for pulling a business license after the federal government has determined that an employer hired illegal workers, but Arizona?EUR??,,????'???s law empowers the state to act alone.

Although it is already a federal offense to hire illegal workers, the law?EUR??,,????'???s authors contend that more illegal workers will be found because it requires the state?EUR??,,????'???s 15 county attorneys to investigate any complaint they deem not frivolous.

?EUR??,,????'??That?EUR??,,????'???s the problem,?EUR??,,????'?? said Julie A. Pace, a lawyer representing business and advocate groups opposed to the law. ?EUR??,,????'??This is the federal government?EUR??,,????'???s authority, not the state?EUR??,,????'???s.?EUR??,,????'??

But backers of the law say the state?EUR??,,????'???s power to grant business licenses includes the authority to set the criteria for them.

The county attorneys have not taken a position on the law as a group, but they have worked toward developing a uniform process to file and weigh complaints.