Less than two months after the collapse of federal immigration reform efforts, small-business trade and advocacy groups are attacking a looming crackdown on employers that hire workers with fake Social Security numbers.

The move, announced last week by Homeland Security Secretary Michael Chertoff, requires employers to act on discrepancies between employee data and government records within 30 days of receiving a so-called "no match" letter from the Social Security Administration.

Of 250 million wage reports received by the agency every year, up to 4 percent turn up problems with employee Social Security numbers, according to Chertoff.  Last year, the agency issued 138,000 no-match letters.

Starting next month, employers will be required to fire workers that are unable to resolve these problems -- or face hefty fines of up $10,000 per violation.

"The magnet that brings most economic migrants into this country is work," Chertoff said Friday. "If we have worksite enforcement directed at illegal employment, we strike at that magnet."

In announcing the move, Chertoff said employers have to be held accountable "if they are given clear notice of the fact that they may be hiring illegal aliens."

National groups representing small employers say no-match letters are issued for any number of reasons, including spelling errors, name changes as the result of marriage or divorce, or incomplete information in W-2 wage report forms.

The letters even warn employers that they aren't necessarily a reflection of an employee's right to work or immigration status.

As such, the tougher regulations "could make companies liable for knowingly hiring undocumented immigrants based merely on failure to follow procedures that might include laying off United States citizens," according to a the U.S. Chamber of Commerce.

It calls the crackdown a "misguided and untimely" move that shifts the burden of enforcing immigration law onto employers as a result of the failure of legislative reform.

"In the absence of Congressional action, we expected an increase in enforcement pressure on business at the federal, state, and local level, and unfortunately this coming to pass," said John Gay, senior vice president of government affairs for the National Restaurant Association.

Gay said employers are already facing an increasingly tight labor market and are concerned about needlessly letting workers go.

Chertoff said the regulations could result in a gap in employment, given the estimated 12 million undocumented immigrants currently in the U.S. workforce.

"Ultimately, the solution for the problem of filling that gap is a solution that requires congressional action, in terms of temporary work requirements," Chertoff said.