House Democrats took the first steps toward launching an investigation into acting Attorney General Matthew Whitaker for his involvement in a Miami marketing company that allegedly scammed millions of dollars from people looking to sell their inventions.

Reps. Jerrold Nadler, Elijah Cummings, Adam Schiff, and Frank Pallone Jr., the top Democrats on the House Judiciary, Oversight, Intelligence, and Energy and Commerce Committees, sent letters to Whitaker, his former business partner and five other federal and non-federal groups requesting documents and information about the alleged scheme.

House Democrats, who will become the majority when the 116th Congress is sworn in on Jan. 3, have made protecting special counsel Robert S. Mueller III’s investigation into Russia interference in the 2016 election their top oversight priority.

Whitaker, whom President Donald Trump appointed to replace ousted AG Jeff Sessions last week, has taken on the lead advisory role at the Justice Department for the special counsel probe — even though he has publicly antagonized it in the past on cable news outlets like CNN.

Democrats and some Republicans have questioned the constitutionality of Whitaker’s appointment to attorney general since he was never confirmed by the Senate for his previous role at the DOJ. Democrats have questioned Whitaker’s fitness for the office considering his past comments about the special counsel, his level of experience at the DOJ, and his previous business entanglements.

“Because Mr. Whitaker was not confirmed by the Senate, both Republican and Democratic constitutional law experts warned that his appointment was, and continues to be, unconstitutional,” House Democrats said in a joint statement Wednesday.

“Because the Senate was not given an opportunity to properly vet Mr. Whitaker’s background, serious questions are now arising about his fitness to serve in this position of trust,” they said.

In March 2017, the Federal Trade Commission announced it had brought charges against World Patent Marketing for an “invention-promotion scam” in which officials were “deceiving consumers and suppressing complaints about the company by using threats of criminal prosecution against dissatisfied customers.”

Whitaker sat on the company’s advisory board.

The company “promised to promote people’s inventions and took thousands of dollars, but provided almost no service in return,” Maureen Ohlhausen, the acting FTC chairwoman, said at the time.

Per court documents from the case, Whitaker appears to have played a direct role in threatening at least one of the company’s clients.

In one email exchange with a client, Whitaker said that reporting the company to the FTC would incur “serious civil and criminal consequences.”

He also identified himself in the email as a “former United States Attorney for the Southern District of Iowa.”

World Patent Marketing settled with the FTC in May of this year. It accepted a $26 million judgement as well as a permanent ban from the industry.

Spokespeople for the current GOP chairmen for the committees whose Democrats announced the investigation into Whitaker on Wednesday could not immediately be reached for comment.

Watch: Trump Says He Doesn’t Know Matt Whitaker