Read more of our coverage about the Obama administration and immigration reform here.

Many congressional Republicans have threatened to use the budget process to force a government shutdown over President Obama’s pending executive order on immigration, which will be announced Thursday night and is expected to provide relief from deportation to 5 million immigrants.

There’s just one problem with the GOP’s game plan against the president’s action: The House Appropriations Committee said Thursday that it would be “impossible” to de-fund the immigration order.

Committee spokesperson Jennifer Hing explained to reporters that the main agency in charge of carrying out Obama’s action, the U.S. Citizens and Immigration Services (CIS) agency, is funded entirely through immigration application fees.

“We cannot, literally cannot, de-fund that agency in an appropriations bill because we don’t appropriate that agency. That agency is entirely fee-funded,” Hing said. “As of right now, our understanding is the primary agency responsible for implementing any type of executive order is CIS and we don’t fund CIS. There are no appropriated dollars.”

In other words, because CIS is not funded by Congress, the GOP-led Congress can’t de-fund it–a claim flatly rejected by some Republican lawmakers furious with the president’s executive order.

This doesn’t mean Congress is powerless to change the funding of CIS, which is responsible for issuing immigration status and work permits. It does, however, mean Congress can’t force the measure through by using the appropriations process. And using that process is the only way to truly force Obama’s hand on immigration.

Obama could easily veto any stand-alone bills Congress might pass, but if an anti-immigration bill was attached to a must-pass spending bill, vetoing that would ultimately lead to a government shutdown.

Congress must pass a bill funding the government, whether short-term or long-term, by December 11.

Several prominent Republicans on Thursday dismissed the idea that Congress can’t block funding for the executive order.

Brian Phillips, spokesperson for Sen. Mike Lee (R-UT), told Rewire that these claims are “nonsense,” adding that “House Leadership said the same thing about de-funding Obamacare last year and then Rep. Grave somehow found a way to write the language.”

Sen. Jeff Sessions (R-AL) claimed there is “no question that Congress has the power to block this expenditure.”

“I just don’t believe that,” Rep. Steve King (R-IA) told reporters in response to the argument from the appropriations committee.

King is one of many Republicans who have made extreme statements in recent days about the effects of Obama’s pending action on immigration.

King said Wednesday that the president is “throwing this nation into a crisis,” and has said that he “would not rule out” impeachment.

Sen. Tom Coburn (R-OK) speculated that “you could see violence” in the wake of the order, and that it could worsen racial tensions in Ferguson, Missouri.

Sen. Ted Cruz (R-TX) on the Senate floor Thursday compared Obama to a would-be murderous conspirator in ancient Rome, reading a modified version of a famous Cicero speech to accuse Obama of “plotting” and being “openly desirous to destroy the Constitution.”

Continuing the tyranny theme, Sen. Rand Paul (R-KY) called Obama a “president who thinks he’s a king.”

Meanwhile, the secretary of state of Kansas suggested Obama was promoting anti-white “ethnic cleansing.”

Sen. Patrick Leahy (D-VT) called conservative claims that executive action is illegal “balderdash” on the Senate floor Thursday, noting that every president since Eisenhower has taken executive action on immigration reform.

“Our system will not fix itself, and it should be no surprise that the president has decided to use his authority to make our country safer, stronger, and more humane,” Leahy said.