The Bush administration said on Friday it would increase scrutiny and impose heftier fines on U.S. businesses that employ illegal immigrants as it sought to step up enforcement despite Congress's failure to reform immigration laws.

Employers who ignore immigration laws will face an increased likelihood of criminal charges and 25 percent higher penalties, Homeland Security Secretary Michael Chertoff said.

Chertoff said the new effort was the most the government could do to fight illegal immigration as long as Congress does not act.

These are ... not the best tools we can use, Chertoff said at a news conference. This is kind of a half measure.

Congress failed to pass a comprehensive overhaul of immigration laws in June despite heavy lobbying by the Bush administration.

The new enforcement effort could create headaches for farms, restaurants, construction companies and other businesses that rely on low-skilled immigrant workers.

The U.S. Chamber of Commerce said the effort would impose new costs on businesses, and the AFL-CIO labor group said it could give abusive employers more power over workers.

Employers must currently verify that their workers are in the United States legally by collecting their Social Security numbers and immigration documents. Those numbers are checked against the U.S. government's database, and employers are notified of those that don't match up.

Under the new rule, which will take effect in 30 days, employers notified of a mismatch will have 90 days to confirm that the employee is in the country legally, or fire them if not.

Those who do not comply could face fines of up to $12,500 per violation, a 25 percent increase over the existing maximum, as well as possible criminal charges.

Employers will be encouraged to use a new electronic system to check workers' immigration status. New government contractors will be required to use the system.

The government has already stepped up raids of companies that use illegal immigrant workers, deporting a record 185,421 in fiscal year 2006.

Criminal investigations of employers have increased dramatically as well, with 742 arrests since October.

The government also will streamline seasonal worker programs and expand the visa term for professional workers from Mexico and Canada from one year to three years and add 1,700 border guards.

But these efforts alone will not stop illegal immigration, Commerce Secretary Carlos Gutierrez said.

We do not have the workers our economy needs to keep growing each year, Gutierrez said. Ultimately Congress is going to have to pass comprehensive immigration reform.

There are an estimated 12 million illegal immigrants living in the United States.