Senator Mike Lee, R-Utah, attends a Senate Judiciary Committee hearing in Washington, DC, on September 29, 2021.
CNN  — 

All but six Senate Republicans on Saturday vowed to oppose raising the debt ceiling “without substantive spending and budget reforms,” backing up House Speaker Kevin McCarthy’s position.

The group of 43 Republican senators, led by Sen. Mike Lee of Utah, 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 a letter to Senate Majority Leader Chuck Schumer, a New York Democrat.

The letter underscores the deep rift in Washington over how to avoid a debt default. Republicans have repeatedly advocated spending cuts tied to the debt ceiling while the White House has maintained it will not negotiate on the matter.

Sens. Susan Collins of Maine, Lisa Murkowski of Alaska, Mitt Romney of Utah, Rand Paul of Kentucky, Josh Hawley of Missouri and John Kennedy of Louisiana are the only Republicans in the chamber to not sign on to the letter.

A breach of the US debt ceiling risks sparking a 2008-style economic catastrophe that wipes out millions of jobs and sets America back for generations, Moody’s Analytics has warned. The impact could include delayed Social Security payments, late paychecks for federal employees and veterans and a direct hit to Americans’ investments.

Treasury Secretary Janet Yellen said the US could default on its debt as soon as June 1 if Congress doesn’t act.

“Our economy is in free fall due to unsustainable fiscal policies,” the senators write in the letter. “This trajectory must be addressed with fiscal reforms. Moreover, recent Treasury projections have reinforced the urgency of addressing the debt ceiling. The House has taken a responsible first step in coming to the table with their proposals. It is imperative that the president now do the same.”

“As such, we will not be voting for cloture on any bill that raises the debt ceiling without substantive spending and budget reforms,” they add.

The White House fired back Saturday, accusing the Republican senators of holding the economic livelihood of millions of Americans hostage.

“At a moment when the country just posted historic jobs gains, this is no time for these Senators to reverse their support for avoiding default without conditions during the Trump presidency,” White House deputy press secretary 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.”

“The American people would not stand for that threat under any circumstances, but especially not to allow the draconian cuts in the House bill that would throw veterans, law enforcement, manufacturing workers, and sick children under the bus,” Bates added.

President Joe Biden is set to sit down with McCarthy, a California Republican, and other congressional leaders on Tuesday to discuss raising the debt ceiling.

Earlier this week, the White House expressed openness to a short-term fix to the debt ceiling but later walked back the position.

Office of Management and Budget Director Shalanda Young reiterated to reporters this week that the administration’s position remains that “It is Congress’ duty to ensure we don’t default.”

“Congress can put a bill on the floor tomorrow, avoid default,” Young said during a White House briefing Thursday. “The DC drama, the political brinksmanship. That’s what that is. Nothing is preventing Congress from moving to avoid default. And they need to do that, whether it’s tomorrow or next week.”

This story has been updated with additional information.

CNN’s Kaanita Iyer, Betsy Klein, Tami Luhby and Elisabeth Buchwald contributed to this report.