USDA says SNAP benefits won't be issued on Nov. 1

Employees who worked in various departments at the Centers for Disease Control and Prevention were terminated as part of Trump's Friday Reductions in Force order, sources told ABC News Friday.

Among the departments affected were: the National Center for Immunization and Respiratory Diseases; the Global Health Center; the Alzheimer's Disease Program; Office of Public Health Data, Surveillance, and Technology; the Injury Center, the Epidemic Intelligence Service; the Center for Forecasting Outbreaks and Analytics; the Public Health Infrastructure Center and the National Center for Chronic Disease Prevention; and Health Promotion.

The RIFs appear to be impacting communications teams at the CDC as well as scientists, according to the sources.

It’s possible some staff who were terminated were not among the employees furloughed during the federal government shutdown, the sources said.

-ABC News' Mark Abdelmalek and Mary Kekatos

The Trump administration has provided more details about which federal agencies have sent out "reduction in force" (RIF) notices to workers amid the government shutdown and how many total workers have been impacted.

The Office of Management and Budget said over 4,000 workers across seven federal agencies received the layoff notices, according to a filing in a joint lawsuit from the American Federation of Government Employees and the AFL-CIO

In the filing, OMB said the Departments of Treasury, Health and Human Services, and Education have sent the most notices, as of Friday evening.

The following Defendant agencies began issuing RIF notices related to the lapse in appropriations as of today, according to the filing:

• Commerce: approximately 315 employees
• Education: approximately 466 employees
• Energy: approximately 187 employees
• Health and Human Services: approximately 1,100 and 1,200 employees
• Housing and Urban Development: approximately 442 employees
• Homeland Security: approximately 176 employees
• Treasury: approximately 1,446 employees

The Environmental Protection Agency also issued a general "intent to RIF" notice to approximately 20 to 30 employees on Friday, notifying them that they may be affected by a RIF in the future.

-ABC News' Isabella Murray

President Donald Trump confirmed mass firings of federal workers began Friday amid the government shutdown and said the layoffs would be "Democrat-oriented."

Earlier, White House Office of Management and Budget Director Russ Vought said in a social media post "The RIFs have begun," referring to reductions-in-force.

Speaking to reporters from the Oval Office on Friday, Trump did not specify which agencies were laying off workers or the exact number of layoffs but said it would be "a lot."

Trump continued to lay blame for the shutdown on Democrats in Congress.

"They started this thing so it [layoffs] should be Democrat-oriented," Trump said.

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