Six Republican senators are sending a letter to President Donald Trump Tuesday asking him to oppose any congressional effort to restore earmarks.

The letter from GOP Sens. Jeff Flake and John McCain of Arizona, Ted Cruz of Texas, Mike Lee of Utah, Rand Paul of Kentucky and Ben Sasse of Nebraska comes as House Republicans are expected to soon begin holding hearings on the idea of allowing earmarks to make a comeback after congressional Republicans, led by then-Speaker John A. Boehner, banned them in 2011.

“Earmarks represent the pay-to-play culture you have pledged to end,” the senators said in the letter, an early copy of which was provided to Roll Call. “It is unfathomable to those of us who fought to end earmarks and witnessed our colleagues go to jail for corruption that pork barrel politics would return, especially at this time when Americans are clearly fed up with business-as-usual.”

The earmark debate resurfaced last year when a few House Republicans sought to add an amendment to their conference rules packaging to allow a limited restoration of earmarks. Speaker Paul D. Ryan urged the conference not to vote on such a change behind closed doors. In exchange, he pledged to revisit the issue early this year.

To honor that promise, the House Rules Committee is expected to soon begin a series of hearings on the matter. Rules Chairman Pete Sessions of Texas said last month that the committee would hold a series of hearings – none of which have yet been scheduled – and then issue a recommendation on whether House Republicans should move to soften the current ban.

A Rules Committee aide said the panel is still working on scheduling hearings with witnesses from all sides of the issue and does not yet have a timeline.

Flake, McCain, Cruz, Lee, Paul and Sasse said in their letter to Trump that with the national debt set to soon top $20 trillion, “processing thousands or even hundreds of pork requests will only distract and delay addressing pressing national needs and push spending decisions once again into the murky shadows.”

“We respectfully urge you to make it clear that you will veto any bill Congress sends to you containing earmarks within the legislative text or the accompanying report,” the senators said. “We look forward to working with you to make Washington more accountable and stop wasteful spending where it starts, which is often right here in Congress.”