Sen. Jeff Sessions (R-Ala.) last week expressed outrage when U.S. Citizenship and Immigration Services announced plans for hiring 1,000 full-time employees to carry out President Obama’s controversial new immigration actions, which will shield an estimated 5 million immigrants from deportation.

But Republican lawmakers have little power to stop the hiring spree, even when they take control of the Senate next year and hold majorities in both chambers of Congress. That’s because USCIS survives largely on fees rather than legislative appropriations, meaning the agency is largely immune to the power of the purse.

About 95 percent of USCIS’s annual budget comes from fees that immigrants pay to have their applications processed. The main exceptions are the agency’s citizenship offices and its E-Verify operations, which help employers verify work eligibility.

USCIS’s budget is so unaffected by congressional appropriations that most of the agency’s employees worked through last year’s government shutdown.

Congress can starve certain agencies of funding if it doesn’t approve of their programs, but that’s not the case with USCIS and its hiring initiative. USCIS announced last week that it was looking to start a new operational center in Arlington, Va., with about 1,000 full-time, permanent employees whose initial workload will include processing cases filed because of Obama’s immigration actions.

Sessions called the plans for a new facility “a clear symbol of the president’s defiance of the American people, their laws and their constitution.” He added that Obama is “hiring federal employees to carry out a directive that violates the laws Congress has passed in order to foist on the nation laws Congress has repeatedly refused to pass.”

Although Republicans cannot do much to prevent the new wave of USCIS hiring, they are working on a strategy to stifle the president’s overall immigration plan.

House Speaker John Boehner last week laid out an approach that includes banning the White House from changing U.S. immigration policies unilaterally and funding the Department of Homeland Security only through February in an effort to force compromise from Obama.

The House approved the ban in a vote last week, but the measure is likely to die in the Democrat-controlled Senate, and the White House has said it would veto the legislation if it moves to the president’s desk.

Moderate and conservative Republicans have spent the past few weeks debating the advantages and disadvantages of fighting the administration’s new immigration actions once they gain control of the Senate next year, but they can save themselves the trouble when it comes to USCIS’s hiring spree. There’s little they can do about it while Obama is in office.