Republican Sen. Susan Collins, the chair of the Senate Committee on Appropriations, sharply criticized OMB Director Russ Vought's decision to fire federal workers in a new statement released on Friday.

"I strongly oppose OMB Director Russ Vought's attempt to permanently lay off federal workers who have been furloughed due to a completely unnecessary government shutdown caused by Senator Schumer. Regardless of whether federal employees have been working without pay or have been furloughed, their work is incredibly important to serving the public," she said.

"Arbitrary layoffs result in a lack of sufficient personnel needed to conduct the mission of the agency and to deliver essential programs, and cause harm to families in Maine and throughout our country," she added.

-ABC News' Ben Siegel and Mariam Khan

The American Federation of Government Employees, which represents over 800,000 federal employees, blasted the Trump administration over its federal firings, calling them "disgraceful" and "illegal."

"Federal workers are tired of being used as pawns for the political and personal gains of the elected and un-elected leaders. It's time for Congress to do their jobs and negotiate an end to this shutdown immediately," AFGE National President Everett Kelley said in a statement.

"In AFGE's 93 years of existence under several presidential administrations – including during Trump's first term – no president has ever decided to fire thousands of furloughed workers during a government shutdown," he added.

The AFGE filed a lawsuit against the Office of Management and Budget last month over mass firings.

Senate Majority Leader John Thune said the White House is "going to have to do some things" to pay troops amid the ongoing government shutdown but did not specify details.

"I suspect that they're probably going to be, yeah, pretty soon they're going to have to do some things. I think to their credit, the White House has, now for 10 days, laid off doing anything in hopes that enough Senate Democrats would come to their senses and do the right thing and fund the government," Thune said when asked if President Trump should move money around to pay troops.

Thune signaled he was not open to getting rid of the filibuster to allow the Republicans' funding bill to pass with a simple majority, rather than the current required 60 votes, saying it's "something that makes the Senate the Senate."

-ABC News' Fritz Farrow

Employees at the U.S. Department of Health and Human Services were among the layoffs issued Friday, a spokesperson for the agency said.

HHS employees across multiple divisions have received reduction-in-force notices as a direct consequence of the Democrat-led government shutdown," HHS spokesperson Andrew Nixon said.

Nixon blamed "bloated bureaucracy" by the Biden administration for "growing its budget by 38% and its workforce by 17%." The world was still dealing with the COVID-19 pandemic when Biden took office in 2021.

"All HHS employees receiving reduction-in-force notices were designated non-essential by their respective divisions. HHS continues to close wasteful and duplicative entities, including those that are at odds with the Trump administration's Make America Healthy Again agenda," Nixon added.

-ABC News' Cheyenne Haslett