WASHINGTON — A group of 43 Senate Republicans including Minority Leader Mitch McConnell said they’d oppose allowing a vote on legislation increasing the U.S. debt limit with no strings attached, saying “substantive spending and budget reforms” must be part of the package.

The group’s letter to Majority Leader Chuck Schumer included almost every Republican in the chamber and showed they have the votes to block legislation, raising the stakes on President Joe Biden and the Democrats who control the chamber.

“Our economy is in free fall due to unsustainable fiscal policies,” GOP senators said in the letter. “This trajectory must be addressed with fiscal reforms.”

The letter comes amid mounting pressure to raise the $31.4 trillion borrowing limit and avert a catastrophic U.S. payments default. Treasury Secretary Janet Yellen told U.S. lawmakers on Monday that her department’s ability to use special accounting maneuvers to stay within the federal debt limit could be exhausted as soon as June 1.

Biden and top congressional leaders are due to meet Tuesday for highly anticipated talks amid the stalemate. Democrats have said they will negotiate with Republicans on some budget limits, but that it is “hostage-taking” to tie spending cuts to a boost in the debt limit.

The senators who signed have made it clear “that they are holding millions of American jobs, businesses, and retirement accounts hostage,” White House spokesman Andrew Bates said in a statement.

“They need to honor their Constitutional obligation to pay our bills and not unilaterally inflict a recession on the country,” he said.

The Republican-led House in late April passed legislation on a razor-thin 217-215 vote that would hike the debt ceiling by $1.5 trillion – enough to prevent a default until March 31, 2024 – in exchange for $4.8 trillion in budget cuts. Republicans have indicated it’s an opening offer in talks.

Schumer last week put a clean debt-ceiling bill on the roster for possible Senate action at some point.

Sen. Mike Lee of Utah, the Republican who led the effort behind the new GOP letter, said in a statement on Saturday it shows that “Senate Republicans aren’t going to bail out Biden and Schumer, they have to negotiate.”

Republican senators who didn’t sign the letter included a cluster of moderates – Susan Collins, Lisa Murkowski of Alaska, and Mitt Romney of Utah.