Two Democratic senators are asking Attorney General Merrick Garland to appoint a special counsel to investigate Supreme Court Justice Clarence Thomas for possible tax law violations.

Sens. Sheldon Whitehouse (D-R.I.) and Ron Wyden (D-Ore.) sent the letter to Garland last week asking him to appoint a special counsel “to investigate possible violations of federal ethics and tax laws.” The two lawmakers pointed to public reporting over the last year which found Thomas failed to disclose multiple luxury trips and gifts from billionaire friends.

“The breadth of the omissions uncovered to date, and the serious possibility of additional tax fraud and false statement violations by Justice Thomas and his associates, warrant the appointment of a Special Counsel to investigate this misconduct,” the lawmakers wrote.

The lawmakers noted that the Senate cannot prosecute Thomas and that the Supreme Court “has no fact-finding function of its own.” They said that the failure to disclose outside income and the luxury gifts warrants a criminal investigation.

They referenced an investigation by Wyden’s office last year which found Thomas did not pay the principal of a $267,230 loan he used to purchase a motorcoach.

The investigation suggested that the loan was forgiven, but Thomas’s attorney disputed that at the time, saying Thomas satisfied the terms of the agreement. The lawmakers raised questions in the letter over whether Thomas reported the apparent forgiveness of the loan on his tax returns

“Justice Thomas failed to clarify whether or why he failed to report hundreds of thousands of dollars in forgiven debt on his federal income tax returns and pay the income taxes owed. We submit that the facts we have developed, combined with strategically evasive answers, creates predication for further investigation by relevant authorities,” the letter said.

Whitehouse and Wyden noted they did “not make this request lightly.”

“The evidence assembled thus far plainly suggests that Justice Thomas has committed numerous willful violations of federal ethics and false-statement laws and raises significant questions about whether he and his wealthy benefactors have complied with their federal tax obligations,” they wrote.

“Presented with opportunities to resolve questions about his conduct, Justice Thomas has maintained a suspicious silence,” they continued.

The Hill has reached out to the Supreme Court and the Department of Justice for comment.