PORTSMOUTH, N.H. — There are about 645 probationary employees at the Portsmouth Naval Shipyard who are anxiously awaiting news of whether their positions are among those being eliminated in a purge of the federal workforce.

That tally is according to members of New Hampshire’s congressional delegation who joined union leaders in Portsmouth on Friday to urge the Trump administration and the Department of Defense to spare the shipyard from the restructuring of the federal government that has eliminated thousands of federal workers.

They argued that any reduction in the shipyard’s workforce, currently about 8,000 strong, would compromise national security. Shipyard workers maintain the US Navy’s fleet of submarines and make sure they’re able to deploy when called upon.

“The skilled tradespeople of this shipyard are not just another workforce. We are a cornerstone of national security,” said Nathan Proper, president of the United Brotherhood of Carpenters and Joiners of America Local 3073.

“We build, maintain, and repair the fleet that protects America’s interests around the world,” he said. “Without us, the Navy doesn’t sail. Without us, submarines don’t deploy.”

The shipyard, located in Kittery, Maine, is also a major employer and economic driver for communities in southern Maine and the seacoast region of New Hampshire. It paused recruiting and hiring efforts amid uncertainty over federal layoffs.

Defense Secretary Pete Hegseth said that across the agency about 5,400 probationary workers would be fired starting last week, and that a hiring freeze would follow. He said there would be a broader 5 percent to 8 percent reduction to the civilian workforce.

“Our workforce has been terrorized by reckless threats of firings, layoffs, repercussions for actions that have nothing to do with them,” said Alana C. Schaeffer, president of the Portsmouth Federal Employees Metal Trades Council, which represents about 3,600 shipyard employees, 464 of whom are probationary.

New hires are often considered probationary before they complete one year on the job, but some workers are considered probationary after switching jobs or receiving a promotion.

Schaeffer said information about potential layoffs has been slow and inconsistent, causing chaos, frustration, and confusion among employees.

Senator Jeanne Shaheen and Congressman Chris Pappas said Friday they are urging the Department of Defense to exempt the shipyard from cuts and layoffs.

Proper said that historically such exemptions have been granted, “because the work we do is too important to be disrupted by political whims.”

Steven Porter of the Globe staff contributed to this report.

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Amanda Gokee can be reached at amanda.gokee@globe.com. Follow her @amanda_gokee.