A group of Democratic lawmakers announced on Wednesday that they are launching an investigation into acting Attorney General Matthew Whitaker's involvement in a company the government deemed a scam.

"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," Reps. Elijah Cummings Elijah Eugene CummingsBlack GOP candidate accuses Behar of wearing black face in heated interview Overnight Health Care: US won't join global coronavirus vaccine initiative | Federal panel lays out initial priorities for COVID-19 vaccine distribution | NIH panel: 'Insufficient data' to show treatment touted by Trump works House Oversight Democrats to subpoena AbbVie in drug pricing probe MORE (Md.), Jerrold Nadler (N.Y.) , Frank Pallone, Jr. (N.J), and Adam Schiff Adam Bennett SchiffPelosi, Democrats unveil bills to rein in alleged White House abuses of power Chris Matthews ripped for complimenting Trump's 'true presidential behavior' on Ginsburg Trump casts doubt on Ginsburg statement, wonders if it was written by Schiff, Pelosi or Schumer MORE (Calif.) said in a joint statement.

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"In addition, 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."

The Democrats who signed the statement are likely to to become chairmen of the House Oversight, Judiciary, Intelligence and Energy and Commerce Committees in the next Congress.

The lawmakers said that they sent seven letters in hopes of receiving documents about Whitaker's role at World Patent Marketing. The letters were sent to people including Whitaker and the former founder and CEO of the company.

Court filings indicate that Whitaker received regular payments of $1,875 while serving on the company's advisory board.

His role has gained growing scrutiny in the past week since Whitaker was appointed. The Federal Trade Commission (FTC) ordered the company to pay a $26 million settlement in May after accusing it of duping aspiring inventors.

The lawmakers also voiced concerns over reports that Whitaker sent a threatening email to a former customer who had complained about the company in August 2015.

A spokesperson for the Justice Department told CNN last week that Whitaker "has said he was not aware of any fraudulent activity."

Trump announced last week that Whitaker would take over as acting attorney general after Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE resigned at the president's request. His past business dealings have been under increasing scrutiny since.