Democrats on the House committees on Intelligence and Oversight on Tuesday urged the Defense Department inspector general to open an investigation into whether the Trump administration retaliated against the now-retired Army lieutenant colonel who testified against President Trump during his impeachment proceedings.

House Oversight Committee Chair Carolyn Maloney, D-N.Y., and House Intelligence Committee Chairman Adam Schiff, D-Calif., along with Rep. Stephen Lynch, D-Mass., the chairman of the Oversight Committee’s subcommittee on National Security, penned a letter to Pentagon acting Inspector General Sean O’Donnell urging him to investigate political retaliation against Alexander Vindman, who retired from the Army earlier this month.

LTC ALEXANDER VINDMAN, TRUMP IMPEACHMENT WITNESS, RETIRES FROM MILITARY

“Retaliation against a talented and dedicated war veteran is completely unacceptable and sends the wrong message to our fellow Americans in uniform about the oaths they take to defend and protect the Constitution,” they wrote. “It is critical that your office act now to investigate these allegations to ensure that our military system remains impervious to political vendettas.”

Maloney, Schiff and Lynch urged O’Donnell to examine the actions involving the employment, career opportunities or promotion of Vindman following his testimony before Congress, and whether they were influenced by White House officials.

The chairs also requested a full investigation into any actions to create “retaliatory work environment” for Vindman, including “retributive actions taken” against him and his brother, and “systemic improvements” that could be made to protect whistleblowers in the future.

The letter to the inspector general comes just weeks after Vindman announced his retirement, after having served for 21 years in the military. Vindman retired because "it has been made clear that his future within the institution he has dutifully served will forever be limited," David Pressman, Vindman's lawyer, said.

In a statement, Pressman said Vindman was bullied by Trump and his proxies for answering a subpoena from Congress to testify.

Vindman was an important witness for Democrats during the House impeachment inquiry. He raised concerns over Trump’s July 25 phone call urging Ukraine's president to look into the country's decision to oust a prosecutor who had been investigating the natural gas firm Burisma Holdings — where Joe Biden's son Hunter Biden was on the board.

"LTC Vindman’s patriotism has cost him his career," said Pressman, a former ambassador to the United Nations for Special Political Affairs. "Today our country loses a devoted soldier, but it is incumbent upon all of us to ensure it does not lose the values he represents.”

IMPEACHMENT WITNESS VINDMAN FIRED, ESCORTED OUT OF WHITE HOUSE AFTER TRUMP ACQUITTAL

Congressional Democrats have accused Trump of retaliating against impeachment witnesses, including Vindman and U.S. Ambassador to the European Union Gordon Sondland, who was recalled from his position.

In February, Vindman was fired from his post at the National Security Council and was escorted off of the White House grounds, after the president’s acquittal.

Trump said in February that Vindman needed to go because he was "very insubordinate" and misrepresented his "perfect" call with Ukrainian President Volodymyr Zelensky.

Also that day, Sondland announced that he had been recalled from his post.

Maloney, Schiff and Lynch have given O'Donnell a deadline of July 24 to advise on whether he will open an investigation into the allegations.

Fox News' Marisa Schultz contributed to this report.