The department is opposing testimony by Aaron Zebley and James Quarles before the Democratic-led Judiciary and Intelligence committees in the House of Representatives, two sources said.
The men were expected to testify on July 17, the same day that Mueller is due as a witness before the two panels.
Democrats said they still expect Zebley and Quarles to appear, arguing that the Justice Department has no authority over the behavior of former employees. But a third source told Reuters that the former Mueller team members were still negotiating with the committees.
“We expect them to appear,” Representative Zoe Lofgren, a Democratic member of the Judiciary Committee, told reporters. “We’ve got two hours with the Judiciary and Mr. Mueller, and two hours for the Intel committee with Mr. Mueller, and then some time afterwards with his staff.”
Justice Department officials had no immediate comment and Zebley and Quarles could not be reached for comment.
The episode is the latest example of Trump administration efforts to stymie congressional investigations by directing current and former officials not to cooperate with investigators who are seeking evidence of corruption, obstruction of justice and abuse of power in the Trump presidency.
House Judiciary Democrats, who are poised to expand their probe of Trump, his family and associates with a slew of new subpoenas, say Mueller’s testimony will focus public attention on some of the more disturbing findings of his two-year investigation of Russian meddling in the 2016 presidential election.
In a 448-page report, Mueller said the Trump campaign had numerous contacts with Moscow though the investigation did not find sufficient evidence to show conspiracy.
He did not conclude that Trump obstructed justice by trying to impede the Russia probe, but also did not exonerate the president of doing so.
The House Judiciary Committee is also investigating alleged hush payments during the 2016 campaign to two women who claimed to have affairs with Trump, including porn star Stormy Daniels.
“The Dems Witch Hunt continues!” Trump said in a tweet on Wednesday. He has regularly denounced the Mueller investigation while also claiming that the probe found “no collusion” with Russia and “no obstruction.”
Judiciary Committee Democrats privately met on Wednesday to discuss details of conducting the Mueller hearing and his aides’ testimony, Democrats on the panel said.
Representative Adam Schiff, who leads the intelligence committee, said he expects the special counsel’s office to live up to the agreements for Mueller and his aides to testify.
Mueller, in his first public comments since starting his investigation, said on May 29 that Justice Department policies meant the probe was never going to end with criminal charges against Trump, and indicated it was up to Congress to decide whether he should be impeached.
“If we had confidence that the president clearly did not commit a crime, we would have said so,” Mueller said.
Reporting by David Morgan, Richard Cowan and Doina Chiacu; Editing by Bernadette Baum and Bill Trott