(CNN) House Democrats are kicking off their investigations into the Trump administration by probing acting Attorney General Matt Whitaker's connections to a Florida company that was shut down by the Federal Trade Commission over what court documents called "a scam that has bilked thousands of consumers out of millions of dollars."

The top Democrats on the House Oversight, Judiciary, Intelligence and Energy and Commerce Committees jointly sent seven letters requesting documents and briefings about Whitaker's role on the advisory board of the company, World Patent Marketing, which was hit with a $26 million judgment when it was shut down earlier this year.

The letters represent an opening salvo of how House Democrats plan to investigate the Trump administration when they take over in January. The letters from the four presumptive incoming chairmen — Reps. Elijah Cummings of Oversight, Jerry Nadler of Judiciary, Adam Schiff of Intelligence and Frank Pallone of Energy and Commerce — suggest the committees are preparing, at least initially, to jointly investigate targets that multiple panels are interested in.

Whitaker's appointment following the firing of Jeff Sessions last week has been slammed by Democrats as potentially unconstitutional, as well as an effort to undermine special counsel Robert Mueller, whose investigation Whitaker has publicly criticized.

"Our very first witness after January 3, we will subpoena, or we will summon, if necessary subpoena, Mr. Whitaker," Nadler told CNN's Jake Tapper Sunday on "State of the Union."