• Two Democratic Senate committee leaders are seeking a special counsel investigation into whether Supreme Court Justice Clarence Thomas broke federal tax and ethics laws.
• Senate Finance Committee Chair Ron Wyden, D-Ore., and Sen. Sheldon Whitehouse, D-R.I., who leads a subcommittee on federal courts, asked Attorney General Merrick Garland to make the appointment.
• Evidence suggests Thomas has "secretly accepted gifts and income potentially worth millions of dollars" since he joined the high court, the senators alleged.

Two Democratic Senate committee leaders asked the Department of Justice to appoint a special counsel to investigate whether Supreme Court Justice Clarence Thomas broke federal tax and ethics laws, the senators said Tuesday.

"We do not make this request lightly," said Senate Finance Committee Chair Ron Wyden, D-Ore., and Sen. Sheldon Whitehouse, D-R.I., who leads a subcommittee on federal courts, in a letter sent to Attorney General Merrick Garland last week.

"The evidence assembled thus far plainly suggests that Justice Thomas has committed numerous willful violations of federal ethics and false-statement laws," the senators alleged in the letter.

It also "raises significant questions about whether he and his wealthy benefactors have complied with their federal tax obligations," Wyden and Whitehouse wrote.

That evidence, they wrote, suggests that Thomas "likely violated federal law by accepting lavish gifts from wealthy benefactors and failing to report them" in violation of the Ethics in Government Act.

They pointed to public reporting from ProPublica and other sources, as well as their own Senate investigation, in alleging that Thomas has "secretly accepted gifts and income potentially worth millions of dollars" since he joined the high court in 1991.

Download the letter sent to Garland.

The Supreme Court did not immediately respond to CNBC's request for comment on the letter, which is dated July 3.

Two days before it was written, Thomas in a pivotal court ruling questioned whether the DOJ has the power to even appoint a special counsel.

Thomas' skepticism came in a statement concurring with a majority ruling that former presidents hold absolute immunity for some of their core actions while in office, and "at least presumptive immunity" for all other official acts.

The 6-3 ruling was touted as a win by former President Donald Trump, who had argued that he was immune from prosecution in the federal election interference case being prosecuted by special counsel Jack Smith.

Thomas wrote in his concurrence, "If there is no law establishing the office that the Special Counsel occupies, then he cannot proceed with this prosecution. A private citizen cannot criminally prosecute anyone, let alone a former President."

The court's ruling, which was vehemently opposed by the court's three liberal justices, and Thomas' concurrence threatened to delay or weaken both of Smith's active criminal cases against Trump.