Sen. Mike Lee said he would use “every procedural tool” possible to delay a debt ceiling deal if it doesn’t contain “substantial” cuts, in a tweet published Thursday morning.

Lee’s comments come as House Speaker Kevin McCarthy appears to be trying to moderate expectations over what will be included in the agreement.

“One thing I will tell people is this still won’t solve all the problems. The president took a lot of things off the table, but this will put us in the first step,” McCarthy told Fox News. “Whatever we don’t achieve here, we’ll come back the next day to get it because we’ve got to start working toward being able to balance the budget.”

Negotiations on the debt ceiling are ongoing between McCarthy, R-Calif., and President Joe Biden. With the Senate in recess this week, and without a Senate bill to put up against a bill passed in the House last month, Majority Leader Chuck Schumer has appeared to be less engaged in negotiations than McCarthy and Biden.

Schumer, D-N.Y., may also be facing a difficult path to passing a Senate bill because of the close split in the Senate, combined with the need to have 60 senators on board to pass a bill.

It is also unclear how swing-vote senators like Democratic Sen. Joe Manchin of West Virginia, and independent Arizona Sen. Kyrsten Sinema, would vote on a “clean” bill that would raise the amount the nation is allowed to borrow without any conditions.

Lee sent a letter to Schumer earlier this month that was signed by 43 Republican senators that said they are “united behind the House Republican conference in support of spending cuts and structural budget reform as a starting point for negotiations on the debt ceiling.”

In his tweet, Lee expressed concern that the final deal being hammered out between Biden and McCarthy would not be sufficient, and he vowed to throw up impediments to its passage if it did not go far enough.

“I will use every procedural tool at my disposal to impede a debt-ceiling deal that doesn’t contain substantial spending and budgetary reforms,” he said. “I fear things are moving in that direction. If they do, that proposal will not face smooth sailing in the Senate.”

Lee also published a tweet asking negotiators to keep the REINS Act, which would give Congress the power to review some rules made by federal agencies before they took effect, in the final agreement.

The Republican debt ceiling bill, the “Limit, Save, Grow Act,” passed the House in April largely along party lines. It would cut spending by $4.8 trillion over the next 10 years, according to the Congressional Budget Office. It also included structural reforms, including the REINS Act.

Lee also pushed back on Sen. John Fetterman’s statement that Biden should consider invoking the 14th Amendment to avoid having to negotiate over the debt ceiling.

McCarthy said Monday he had three stipulations for a debt ceiling compromise: they won’t raise taxes, they won’t pass a clean debt ceiling bill, and spending for the year needs to come in lower than last year’s.

Treasury Secretary Janet Yellen has said repeatedly that Congress and the president need to raise the debt ceiling by June 1 in order to avoid a “catastrophe.” But some Republican lawmakers, including Lee, have questioned the strictness of that deadline.

“Congress need not raise the debt ceiling by June 1st to avoid a default,” he wrote earlier this week.

Biden and congressional leaders are getting pressured by lawmakers from the left and right as they try to finalize an agreement. Some lawmakers are also questioning the decision to stick to plans to travel home for Memorial Day weekend, with some, including Rep. Jahana Hayes, D-Conn., saying they should instead stay in Washington, D.C., to finalize an agreement, according to Politico.

House Democrats have criticized Biden’s handling of the negotiations, while the White House says they’re playing “good cop” and allowing Democratic congressional leaders to play “bad cop” in the negotiations, Politico reported.

All 213 House Democrats signed a discharge petition that would force a vote on a clean debt ceiling bill, according to CNN, but they would need five Republicans to sign on in order to bring it to a vote.

At Thursday’s press briefing, White House press secretary Karine Jean-Pierre said the president feels a sense of urgency to reach an agreement in order to avoid a default.