More than 445,000 federal employees saw their union protections disappear in August, as agencies moved to comply with an executive order President Trump signed earlier this year that called for ignoring collective bargaining contracts with nearly one million workers.

The termination of protections followed an Aug. 1 appeals court ruling on legal challenges to Mr. Trump’s directive. The order, signed in late March, directed 22 agencies to ignore contracts for employees in specific unions. Last Thursday, Mr. Trump signed a second executive order stripping union rights from thousands of other employees at six additional agencies.

Mr. Trump said that the affected workers had roles that touched on national security, and that provisions in their labor contracts could interfere with his policies being carried out. He cited, for example, the role that Department of Veterans Affairs employees play in providing care for wounded troops in wartime.

Federal labor unions targeted in the executive orders have repeatedly sued the Trump administration, and in some cases forced the administration to temporarily pause the president’s efforts to shrink the federal work force and reshape the government. The American Federation of Government Employees has filed more than a dozen lawsuits related to the federal work force. The White House has likened this to a declaration of “war.”

So far, nine agencies have terminated union contracts that covered more than 445,000 federal workers from the Environmental Protection Agency, U.S. Coast Guard, Federal Emergency Management Agency, General Services Administration, the Departments of Health and Human Services, Agriculture and Veterans Affairs, and parts of Immigration and Customs Enforcement and Citizenship and Immigration Services.

“This is literally the largest act of union busting in American history,” said Mike Podhorzer, a former political director of the A.F.L.-C.I.O. “There’s not another time when that many people lost their union.”