EXCLUSIVE: A group of 21 House conservatives warned House Speaker Kevin McCarthy on Monday that they won't be voting for appropriations bills this year unless they reflect a real effort to trim excess federal spending, a threat that will likely complicate GOP efforts to fund the government.

The warning shot signals another looming fight McCarthy may have to have in public with the right flank of his party. Dozens of conservatives voted against the spending deal McCarthy reached with President Biden earlier this year, which only promised modest cuts to federal outlays that fell short of a GOP-backed bill that passed the House.

In a letter send Monday, they said that deal won't be good enough to win their support when spending bills come up for a vote this year. That's a significant problem for McCarthy, who can only afford to lose a handful of GOP votes if he wants to pass legislation without help from Democrats.

"We cannot support appropriations bills that will produce a top-line discretionary spending level barely below the bloated FY 2023 level… and effectively in line with the cap set by the debt ceiling deal that we opposed and was supported by more Democrats than Republicans," the conservative members wrote in their letter that was obtained by Fox News Digital.

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Lauren Boebert, Kevin McCarthy, Chip Roy

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"Instead, we expect all appropriations measures… to be in line with the enacted FY 2022 topline level of $1.471 trillion," they wrote.

They also said they would not support the idea of using rescinded unspent COVID-19 funding to exceed fiscal year 2022 levels.

"Rescissions are useful in reducing spending and we encourage their use, but we cannot support using them to shift funding to the very bureaucrats implementing the Biden agenda at roughly current levels of spending, thereby enshrining and continuing Democrats’ reckless inflationary spending," they wrote.

The letter was led by House Freedom Caucus Chair Scott Perry, R-Pa., but it's not a formal HFC position as other Republicans signed onto the letter who aren't members of that caucus.

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It stressed to McCarthy that voters expect results over party unity, another warning shot that they are prepared to vote against GOP leadership in order to get those results.

"Americans expect House Republicans to lead in divided government to achieve tangible results. They do not care about unity absent unity of purpose and achievement. They expect us to go beyond the theater of hearings, messaging bills that die in the Senate, or very modest spending limits in the wake of record inflationary spending levels," said the letter.

"For unity to exist, we must have a clear mission to actually cut the total discretionary federal bureaucracy to pre-pandemic levels and end the empowerment of President Biden’s radical woke and weaponized government," they added.

Last month, opponents of the bipartisan debt limit deal brought House floor proceedings to a grinding halt for nearly a week in protest over not feeling heard by GOP leadership.

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House and Senate leaders meet with Biden

McCarthy has seen rebellions from his right flank since striking a deal on the debt limit with President Biden (Anna Moneymaker/Getty Images)

The conservatives' letter calls on McCarthy to hold votes on spending bills this year until all 12 are made public so that lawmakers and Americans "can assess total spending levels and their impact."

It also demands a public assurance from McCarthy opposing supplemental Ukraine aid that would make Defense spending exceed fiscal 2022 levels. That’s nearly guaranteed to set up a battle in the Senate, where a majority of the GOP conference supports helping Kyiv fight off Russia’s invasion.

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"We intend to keep the promises we made to the American people to cut federal spending, reduce the  size and scope of the woke and weaponized federal bureaucracy, and ensure their security," the conservatives said. "And we stand ready to work with you to use the power of the purse to force the President to the table to work with us to make good on these promises.".

In addition to Perry, the signatories include Reps. Chip Roy of Texas, Byron Donalds of Florida, Lauren Boebert of Colorado and Dan Bishop of North Carolina. An early draft of the letter was published by Politico last week.