WASHINGTON -- The House Appropriations Committee confirmed Thursday what some people are already figuring out: Republicans don't have the ability to defund President Barack Obama 's forthcoming executive action on immigration.

Obama is expected to announce Thursday night that he will use his executive authority to stop deportations for as many as 5 million undocumented immigrants. Republicans have fumed about the president going around Congress to make such a significant change and vowed to cut off funding for it . Some have even threatened to shut down the government in protest.

But lawmakers can't cut off funding for Obama's action because the agency responsible for carrying out the changes is completely self-funded, the House Appropriations Committee explained in a statement:

"The primary agency for implementing the President's new immigration executive order is the U.S. Citizenship and Immigration Services (USCIS). This agency is entirely self-funded through the fees it collects on various immigration applications. Congress does not appropriate funds for any of its operations, including the issuance of immigration status or work permits, with the exception of the 'E-Verify' program. Therefore, the Appropriations process cannot be used to 'de-fund' the agency. The agency has the ability to continue to collect and use fees to continue current operations, and to expand operations as under a new Executive Order, without needing legislative approval by the Appropriations Committee or the Congress, even under a continuing resolution or a government shutdown.

The president's decision to take unilateral action comes in response to Congress' failure to pass comprehensive immigration reform. The Senate passed a bipartisan bill more than a year ago, but House Speaker John Boehner (R-Ohio) has refused to give it a vote, leaving the issue on track to stall out at the end of the year.

While many Republicans have said they want to block the president's executive action, they haven't been able to explain how, exactly, they would go about doing it. Sen. Ron Johnson (R-Wis.), for one, has said he has no idea how an effort to cut off funding would work.