The US administration has announced tougher action against businesses which employ illegal immigrants, including more criminal charges and higher fines.
There are an estimated 12 million illegal immigrants living in the US
The tighter workplace enforcement measures come after Congress failed to pass comprehensive immigration reform.
Under the new plan, employers will have 90 days to prove the workers are legal US residents or fire them.
US Homeland Security Secretary Michael Chertoff said the "energetic" step was needed pending action by Congress.
In June senators voted against President George W Bush's immigration reform plan, effectively delaying action on the emotive issue until after the 2008 presidential election.
The proposed legislation called for tougher border controls while setting out ways for illegal immigrants to seek citizenship.
But opponents said the bill amounted to an amnesty for law breakers.
'Not enough workers'
On Friday Mr Chertoff said: "Our hope is that key elements of the Senate bill will see the light of day someday, but until Congress chooses to act we are going to be taking some energetic steps on our own."
He said the new measures would give employers "clear guidance" but added that they were "not the best tools we can use... This is kind of a half-measure."
Mr Chertoff (left) called the efforts "a half measure"
Employers who employ illegal immigrants could face fines of up to $12,500 (£6,250) per violation, a 25% fine increase, as well as possible criminal charges.
The new plan will also strengthen patrols on the Mexican border.
The US government has already stepped up raids on companies employing illegal workers, and the number of criminal investigations of employers has also risen.
However, Commerce Secretary Carlos Gutierrez said such initiatives alone would not stamp out illegal immigration.
"We do not have the workers our economy needs to keep growing each year... ultimately Congress is going to have to pass comprehensive immigration reform."
Correspondents say the measures could have major implications for the country's agriculture, construction and hospitality industries which employ most of the illegal immigrants in the US.