WASHINGTON (Reuters) -Republicans in the U.S. Senate are calling on President Donald Trump's administration to turn to them to make his proposed government spending cuts official in law, rather than unilaterally withholding funds as he has been doing.

Ten Republican Senators representing a broad swath of the party said in interviews they want to see Trump's administration start the legal process called rescission to permanently withhold funds already approved by Congress for fiscal year 2025. This process requires the administration to send specific cuts and their budgetary effect to lawmakers for approval.

The Republican advocacy represents one way some legislators are trying to reassert congressional authority over federal government funding, while at the same time supporting the proposed cuts from Elon Musk's Department of Government Efficiency and in other federal departments. 

"I think the only way to make spending cuts real is to vote on them," said Senator Rand Paul from Kentucky. 

Others this week, noting the process complexity, called for fast action.

"I'd like to be voting on them weekly, if not monthly," said Senator Ron Johnson of Wisconsin, while Senator Chuck Grassley of Iowa said, "I'd like to see it yesterday." 

It is unclear if the administration will start this legislative move, as Russ Vought, who runs the White House Office of Management and Budget, has repeatedly challenged this appropriations process by arguing the underlying 1974 law that established the rescission procedure is unconstitutional. 

That law was put in place following concerns by Congress that Republican President Richard Nixon abused his power by refusing to spend funds authorized by Congress. Trump and Musk so far have bypassed Congress as they have moved to push out more than 100,000 government workers and attempt to close some government departments outright, moves that have drawn legal challenges.

Vought has had a powerful ally in his fight: Trump, who on the campaign trail -- to little fanfare -- promised to challenge this appropriations law. 

TRUMP PROMISED TO CHALLENGE FUNDING PROCESS

The rescission process was established in the Impoundment Control Act of 1974 to give the executive branch a legal and public mechanism to temporarily withhold or permanently eliminate already approved funding by Congress. 

Trump used this process in his first administration but the proposed cuts to foreign aid were rejected by Congress. 

"I will fight to restore the president's historic impoundment power," Trump said at a New Hampshire campaign stop in June 2023, resisting this process. "We are gonna bring it back and we will squeeze the bloated federal bureaucracy." 

After meeting with Republican senators on Thursday, Vought did not respond when asked by a reporter if the White House will send a rescission package to the Hill. In the meeting, Montana's Senator Steve Daines said the discussion included a "very good back and forth" on rescissions.

OMB officials did not respond to a request for comment.

LEGAL AND POLITICAL CHALLENGES 

Rescissions require a simple majority vote in each congressional chamber, both now controlled by Republicans, and could codify the cuts from Musk's Department of Government Efficiency and other federal departments. 

But sending a rescission package now could create a "conundrum" for the administration, said Republican Senator Cynthia Lummis from Wyoming, who advocated for codifying the funding cuts. "It's pretty hard for them to argue in court that it's unconstitutional and then use this so-called unconstitutional provision to implement rescissions."

Gillian Metzger, a constitutional law professor at Columbia University, agreed, saying, "if Congress passes a rescission measure that basically removes that statutory requirement to spend the funds, then the legal basis for the court's ruling is gone."

"The basic fact that Congress has the power of the purse is something Republicans and Democrats agree on," Senator Patty Murray, the top Democrat on the appropriations committee, said in a speech on Thursday. "It won't change no matter what Trump, or Russ Vought, or Elon Musk claim. Their legal theories are plain outlandish and so are their facts."

Murray, along with Republican Appropriations Chair Susan Collins, spoke out against the administration's move this week to partially withhold more emergency funds that were approved by Congress in this month's stopgap funding bill.

The independent and non-partisan government watchdog agency, the Government Accountability Office, started investigating the held-up funds last month, as the 1974 law mandates the agency to do, according to Comptroller General Gene Dodaro. 

David Super, a professor of law and economics at the Georgetown University Law Center, said while some statutes may give the administration more flexibility to withhold funds, the "great majority" -- like funding for U.S. Agency for International Development - do not. "I have no doubt it will be held to be an impoundment," Super said. 

"We got to start codifying the cuts because people back home are pitching a fit about it," Representative Tim Burchett, a Republican from Tennessee, said, "Everywhere I go."