UPDATE: 11:21 a.m., Dec. 20—House Republican Leader Kevin McCarthy promised to enforce the conservatives’ demands if elected speaker in the 118th Congress. Details below.

A group of House conservatives is promising to oppose and stymie the legislative priorities of any Republican senator who votes in favor of the $1.7 trillion omnibus spending bill this week.

The warning shot, delivered via a letter from 13 conservatives Monday night, comes amid rising tensions between Republicans in the House and Senate. In just two weeks, Republicans will control the U.S. House of Representatives, yet passage of the spending bill would severely curtail their efforts to conduct meaningful oversight and hold the Biden administration accountable.

“Senate Republicans have the 41 votes necessary to stop this and should do so now and show the Americans who elected you that they weren’t wrong in doing so,” the lawmakers wrote. “The American people did not elect us—any of us—to continue the status quo in Washington, as this bill will undoubtably do.”

The letter cites several policy areas where House Republicans want to use the “power of the purse” as leverage with the Biden administration. But if at least 10 Republican senators join with Democrats to approve the omnibus spending bill, that leverage evaporates.

>>> Republicans About to Willingly Give Up Their Oversight Leverage Over Biden

The spending bill has the support of House Speaker Nancy Pelosi, D-Calif., and Senate Majority Leader Chuck Schumer, D-N.Y., as well as Senate Minority Leader Mitch McConnell, R-Ky. House Minority Leader Kevin McCarthy, R-Calif., is strongly opposed to the $1.7 trillion spending measure. Last week, during an appearance on Fox News, he reportedly angered his Senate counterparts for speaking out against it.

In a tweet posted Tuesday morning, McCarthy told the 13 conservatives there would be “no need to whip” because “their bills will be dead on arrival in the House” if he’s elected speaker. The full House will vote for speaker Jan. 3 when the 118th Congress convenes.

In their Monday letter, the 13 House conservatives vowed to “oppose and whip opposition to any legislative priority of those senators who vote for this bill—including the Republican leader.”

“We will oppose any rule, any consent request, suspension voice vote, or roll call vote of any such Senate bill, and will otherwise do everything in our power to thwart even the smallest legislative and policy efforts of those senators,” they added.

>>> Omnibus ‘No’ Vote Explains How Democrats Are Trying to Circumvent the Incoming Republican House

With the narrow margin in the House—expected to be 222 Republicans and 213 Democrats in the 118th Congress—just a handful of conservatives could stymie a senator’s priorities.

The 13 conservatives who signed the letter include Reps. Chip Roy, R-Texas; Scott Perry, R-Pa.; Dan Bishop, R-N.C.; Andy Biggs, R-Ariz.; Matthew Rosendale, R-Mont.; Matt Gaetz, R-Fla.; Ralph Norman, R-S.C.; Bob Good, R-Va.; Byron Donalds, R-Fla.; Andrew Clyde, R-Ga.; and Reps.-elect Anna Paulina Luna, R-Fla.; Andy Ogles, R-Tenn.; and Eli Crane, R-Ariz.