Three leading House Democrats said Tuesday that they plan to open an investigation into the replacement of the Transportation Department’s acting inspector general, concerned that the move was tied to an ongoing investigation of Secretary Elaine Chao’s dealings with the state of Kentucky.

Chao is married to Senate Majority Leader Mitch McConnell (R-Ky.) and has faced questions about whether her department has given preferential treatment to projects in the state.

On Friday, President Trump named Howard “Skip” Elliott, the head of a pipeline safety agency, as acting DOT inspector general. Mitch Behm, the department’s deputy, had been filling that role.

In a letter to Chao and Elliott, leaders of the House Oversight and Transportation committees tied Elliott’s appointment to what they called a broad assault by the Trump administration on inspectors general, who serve as internal government watchdogs.

The lawmakers requested information about Chao and her team’s communications with the White House about the decision to replace Behm. They asked Elliott to disclose whether the scope of any of the office’s investigations have changed since his appointment.

“We are concerned that Mr. Behm’s removal could be an effort to undermine the progress of this investigation, which we understand is ongoing,” the lawmakers wrote to Chao. “Any attempt by you or your office to interfere with the Office of Inspector General’s investigation of yourself is illegal and will be thoroughly examined by our Committees.”

In a statement, Chao’s office did not respond to the concerns about the Kentucky investigation but said that the president was within his legal authority to name Elliott acting inspector general.

“Mr. Elliott will bring decades of valuable expertise to the role of Acting Inspector General, both in safety and in law enforcement,” the statement said.

The White House did not respond to a request for comment.

One of the three lawmakers, Transportation Committee Chairman Peter A. DeFazio (D-Ore.), asked the inspector general twice last year to examine whether Chao was giving preferential treatment to Kentucky.

In October 2019, DeFazio said he first requested the inspector general’s office look into Chao’s influence on a discretionary grant program called Infrastructure For Rebuilding America (INFRA). In a December letter to the inspector general, DeFazio amplified his concerns.

“New information has emerged that points to a troubling pattern of potential favoritism by the Secretary and her inner circle of staff at the Department of Transportation (DOT) and has heightened my concern about these issues,” he wrote then.

DeFazio cited news accounts from Politico that he said revealed “that Secretary Chao’s office has degraded the ability of career staff at DOT to objectively assess the merits of grant applications.”

DeFazio also raised questions about Chao’s family’s shipping business and whether she followed her ethics agreement to divest stock in Vulcan Materials, both of which the House Oversight Committee is also investigating.

In Tuesday’s letters, DeFazio along with Reps. Carolyn B. Maloney (D-N.Y.) and Gerald E. Connolly (D-Va.), leaders on the oversight panel, urged Chao to advise the White House to reinstate Behm, whom they called a veteran public servant. Behm took on the role of acting inspector general when the office’s former leader retired in January.

In the letter to Elliott, the lawmakers said they viewed his appointment as part of a broader attack by Trump on inspectors general across the government.

“This assault on the integrity and independence of Inspectors General appears to be an intentional campaign to undermine their ability to expose corruption and protect taxpayer dollars from waste, fraud, and abuse,” the letter said.

The same day he named Elliott to the job at the Transportation Department, Trump removed State Department inspector general Steve Linick. Linick was said to be investigating whether Secretary of State Mike Pompeo had a staffer run nonwork errands for him and to have nearly finished a review of an arms-sale deal with Saudi Arabia.

Elliot had a 40-year career in the railroad industry, serving as an executive at freight company CSX Transportation before joining the Trump administration. The lawmakers questioned what in his professional background qualified him to serve as inspector general.

Elliott is also set to continue as the head of the Pipeline and Hazardous Materials Safety Administration while serving as acting inspector general. The lawmakers wrote that the dual roles would stretch him too thin and presented significant conflicts of interest. The inspector general’s office has at least one open audit that touches on Elliott’s leadership at the pipeline agency, they wrote.

As head of the pipeline agency Elliott reports to Chao, but as inspector general he ought to be independent of the department’s leadership, they said.

“Your dual roles threaten both the safety of our transportation system and the integrity of the DOT Office of Inspector General,” the lawmakers wrote, saying Elliott should resign from one job or the other.

Sen. Tammy Duckworth (D-Ill.), the top Democrat a senate subcommittee that oversees pipeline safety, said she was also concerned about the potential for conflicts of interest in combining the two jobs.

“Acting Inspector General Skip Elliott being charged with auditing and investigating the actions of PHMSA Administrator Skip Elliott makes a mockery of the entire system of Inspectors General,” Duckworth said in a statement.

“Trump’s haphazard approach to firing and hiring Inspector Generals is detrimental to the stability, operations and oversight of the federal government, the Department of Transportation and — most troubling — the entire concept of an accountable, transparent government.”

In the statement, Chao’s office said Elliott would be expected to recuse himself from audits or investigations connected to things that fall under his responsibilities at the pipeline agency.

Jeff Guzzetti, who worked with Behm at the inspector general’s office when they were both senior officials there, said Behm was made the office’s deputy after a rigorous selection process.

“Mitch is organized. He’s sharp as a tack and he gets it,” Guzzetti said.

“He’s very practical and also very ethical,” said Guzzetti, who is now an aviation safety consultant. “He was a kind of a business genius on Wall Street early in his career, and wanted to do something more meaningful through public service and joined the IG, probably making a lot less money.”

On Friday, Trump nominated Eric J. Soskin, a Justice Department attorney, to serve as the permanent inspector general. As the office’s deputy, Guzzetti said Behm was the obvious choice to be its leader until the confirmation of a permanent replacement.

“I can’t for the life of me figure out why he was unceremoniously removed like that, so suddenly,” Guzzetti said, adding that the move to sideline him was a shock.

Guzzetti said that the pipeline safety administration itself has numerous challenges, and the inspector general “is a full-time job.”

“It’s a big agency with a lot on their plate,” he said. “It’s very odd to me. It sounds wrong.”

Tom Hamburger contributed to this report.