LOS ANGELES » A clothing maker with a vast garment factory in downtown Los Angeles is firing about 1,800 immigrant employees in the coming days — more than a quarter of its workforce — after a federal investigation turned up irregularities in the identity documents the workers presented when they were hired.

The firings at the company, American Apparel, have become a showcase for the Obama administration's effort to reduce illegal immigration by forcing employers to dismiss unauthorized workers rather than through workplace raids. The firings, however, have divided opinion in California over the fallout of the new approach, especially at a time of record joblessness in the state and with a major, well-regarded employer as a target.

Mayor Antonio Villaraigosa, a Democrat, called the dismissals “;devastating,”; and his office has insisted that the federal government should focus on employers that exploit their workers. American Apparel has been lauded by city officials and business leaders for paying well above the garment industry standard, offering health benefits and not long ago giving $18 million in stock to its workers.

But opponents of illegal immigration, including Rep. Brian P. Bilbray, R-San Diego, who is chairman of a House caucus that opposes efforts to extend legal status to illegal immigrants, back the enforcement effort. They say American Apparel is typical of many companies that have “;become addicted to illegal labor,”; in Bilbray's words.

“;Of course it's a good idea,”; Bilbray said of the crackdown. “;They seem to think that somehow the law doesn't matter, that crossing the line from legal to illegal is not a big deal.”;

In July, the federal Immigration and Customs Enforcement agency, known as ICE, opened audits of employment records similar to the one at American Apparel at 654 companies around the country. John T. Morton, who, as assistant secretary of homeland security, runs ICE, said the audits covered all types of employers with immigrant workers, including many like American Apparel that were not shadowy sweatshops or serial labor code violators.

The investigation at American Apparel was started 17 months ago, under President George W. Bush. Obama administration officials point out that they have not followed the Bush pattern of concluding such investigations with a mass round-up of workers. Those raids drew criticism for damaging businesses and dividing immigrant families.

Immigration officials said they would now focus on employers, primarily wielding the threat of civil complaints and fines, instead of raids and worker deportation.

“;Now all manner of companies face the very real possibility that the government, using our basic civil powers, is going to come knocking on the door,”; Morton said. The goal, he said, is to create “;a truly national deterrent”; to hiring unauthorized labor that would “;change the practices of American employers as a class.”;

The employees being fired from American Apparel could not resolve discrepancies discovered by investigators in documents they presented at hiring and federal Social Security or immigration records — probably because the documents were fake. Peter Schey, a lawyer for American Apparel, said that ICE had cited deficiencies in its record keeping, but the authorities had not accused the company of knowingly hiring unauthorized workers. A fine threatened by the agency was withdrawn, Schey said.

After months of discussions with ICE officials, the company moved on its own to terminate the workers because, Schey said, federal guidelines for such cases are “;in a shambles.”; The Bush administration proposed rules for employers to follow when workers' documents do not match, but a federal court halted the effort and the Obama administration decided to abandon it.

With its bright-pink, seven-story sewing plant in the center of Los Angeles, American Apparel is one of the biggest manufacturing employers in the city, and makes a selling point of the “;Made in U.S.A.”; labels in its racy T-shirts and miniskirts. Dov Charney, the company's chief executive, has campaigned, in T-shirt logos and eye-catching advertisements, to “;legalize L.A.,”; by granting legal status to illegal immigrants, a policy Obama supports.

ICE has made no arrests so far at the factory. But Morton of ICE said the agency would not rule out pursuing workers proven to be illegal immigrants.

Schey said company human resources managers had added new scrutiny to hiring procedures. But workers facing dismissal pointed to the line of job applicants outside the factory one recent day, who, like many of them, were almost all Spanish-speaking immigrants.

“;I think the Americans think that garment sewing is demeaning work,”; said Francisco, 38, a Guatemalan with nine years at the plant who is being forced to leave.

A top supervisor, he is training new hires to replace him.