(CNN) A group of senators are requesting an investigation into whether FCC Commissioner Michael O'Rielly violated federal law by endorsing President Donald Trump and Republican lawmakers, CNN has learned.

A letter from seven Senate Democrats describes O'Rielly -- a Republican -- answering a question about "regulatory ping-pong" at last month's Conservative Political Action Conference, known as CPAC.

"I think what we can do is make sure as conservatives that we elect good people to both the House, Senate and make sure that President Trump gets reelected," O'Rielly said, according to the letter, which was obtained by CNN.

That, the senators allege, violates the Hatch Act, which prohibits many federal employees from engaging in politics while on the job, in uniform, or using government resources.

"At the time he answered this question, Mr. O'Rielly was appearing in his official capacity and promoting a political candidate who has already filed election paperwork," the senators wrote to the Office of Special Counsel and the FCC inspector general. (The Office of Special Counsel is responsible for investigating potential Hatch Act violations, and is not associated with Special Counsel Robert Mueller.)

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