The chair of the Senate Finance Committee demanded information Monday from a billionaire Republican donor as Democrats respond to reports that Justice Clarence Thomas did not disclose luxury trips and a real estate deal on annual ethics forms.

Sen. Ron Wyden sent a letter to Harlan Crow that requests a detailed accounting by May 8 of private jet flights, vacations and yacht trips Crow provided to Thomas. The Oregon Democrat called it an “unprecedented arrangement between a wealthy benefactor and a Supreme Court justice” that “raises serious concerns.”

“The secrecy surrounding your dealings with Justice Thomas is simply unacceptable,” Wyden wrote. “The American public deserves a full accounting of the full extent of your largesse towards Justice Thomas, including whether these gifts complied with all relevant federal tax and ethics laws.”

Sen. Sheldon Whitehouse of Rhode Island and other congressional Democrats had called for Chief Justice John G. Roberts Jr. to investigate Thomas’ dealings with Crow. But the federal courts responded in a letter Whitehouse released Sunday that the matter has been referred to an ethics committee.

Judge Roslynn R. Mauskopf, director of the Administrative Office of U.S. Courts, wrote that concerns about Thomas had been referred to the Judicial Conference Committee on Financial Disclosure, “which is responsible for implementing the disclosure provisions of the Ethics in Government Act and addressing allegations of errors or omissions in the filing of financial disclosure reports.”

Whitehouse and Rep. Hank Johnson, D-Ga., said in a statement they hope Roberts will agree to testify at a Senate hearing May 2 about “the Court’s ability to enforce the disclosure laws that the justices are subject to.” Johnson is ranking Democrat on the House Judiciary panel with jurisdiction over the courts.

Judiciary Chair Richard J. Durbin, D-Ill., last week invited Roberts to testify about the Supreme Court’s ethics. Durbin said Sunday on NBC’s “Meet the Press” that he would not invite Thomas to testify.

“I think I know what would happen to that invitation. It would be ignored,” Durbin said.

Durbin has said he would focus his efforts on Roberts, pushing the court to adopt an ethics code, a point he reiterated on Sunday.

“History is going to judge the Roberts court by his decision as to reform, and I think this an invitation, on May 2, for him to present it to the American people,” Durbin said.

Some advocates and a handful of Congressional Democrats including Johnson have gone further, calling on Thomas to resign. However, Democrats in Congress have little ability to pressure Thomas or the court to do anything.

Republicans have backed Thomas so far and control the House of Representatives as well as 49 seats in the Senate. Senate Democrats currently cannot subpoena Roberts or Thomas to testify without the help of Republicans, as they lack a majority on the Judiciary Committee because of the absence of Sen. Dianne Feinstein, D-Calif.

Feinstein has been absent from the chamber since February and Republicans have blocked an effort to temporarily replace her on the panel.

Thomas has defended his decision not to disclose the trips, but he has not issued a statement about the lack of disclosure of the real estate transaction.

His statement about the trips cited an exception in normal disclosure rules and referred to Crow and his wife as “among our dearest friends, and we have been friends for over twenty-five years. As friends do, we have joined them on a number of family trips during the more than quarter century we have known them.”

“Early in my tenure at the Court, I sought guidance from my colleagues and others in the judiciary, and was advised that this sort of personal hospitality from close personal friends, who did not have business before the Court, was not reportable,” Thomas said. “I have endeavored to follow that counsel throughout my tenure, and have always sought to comply with the disclosure guidelines.”

Last month, before the ProPublica reports, the Judicial Conference announced a change to its reporting rules, narrowing the exception for “personal hospitality.”