WASHINGTON (AP) — The Senate Judiciary chairman has invited Chief Justice John Roberts to testify next month on ethical standards at the court, a hearing that would undoubtedly focus on business transactions and travel involving Justice Clarence Thomas.

Sen. Richard Durbin, D-Ill., said that there has been a "steady stream of revelations" regarding Supreme Court justices "falling short of ethical standards expected of other federal judges."

"The time has come for a new public conversation on ways to restore confidence in the Court's ethical standards. I invite you to join it, and I look forward to your response," Durbin wrote in a letter Thursday to the chief justice.

Court officials did not immediately reply to a request for comment.

In recent weeks, news reports have focused on the purchase by a conservative donor of three properties belonging to Thomas and his family in a transaction worth more than $100,000 that Thomas never reported, according to the nonprofit investigative journalism organization ProPublica.

ProPublica also previously revealed that Thomas and his wife Ginni were gifted with hundreds of thousands of dollars worth of annual vacations and trips by donor Harlan Crow for decades — including international cruises on his mega-yacht, private jet flights and stays at Crow's invitation-only resort in the Adirondacks. But the 2014 real estate deal is the first public evidence of a direct financial transaction between the pair.

The letter from Durbin asked Roberts — or another justice he chooses to testify instead — to appear before the committee on May 2. He told Roberts that the scope of his testimony would be limited to the ethics rules governing justices of the Supreme Court and potential changes to those rules.

It is rather unusual for sitting Supreme Court justices to testify before Congress. Durbin's letter said the committee most recently heard from sitting justices on Oct. 5, 2011, which he said included "robust exchanges" about ethics matters.

"The opportunity for the American people to hear from Justices in this setting presents a moment that could strengthen faith in our public institutions," Durbin wrote.

Durbin has for years pressed the court to adopt an ethics code, including in that 2011 hearing.

"Do you believe the Supreme Court should be required by law to follow the same financial restriction as everyone else in government?" he asked Justices Stephen Breyer and Antonin Scalia at the hearing in October 2011.

Breyer responded that the justices must file "extensive reports" every year and said he did not think that federal judges lived under more lax rules.

Four years ago, Justice Elena Kagan told a House appropriations panel that Roberts was considering whether to create an ethics code, though nothing has happened since. Kagan was responding to questions about judicial accountability in the MeToo era rather than ethical lapses on the financial front.

Some Senate Republicans are skeptical of the Democratic majority's intentions and see the hearing as mainly an effort to put a critical spotlight on Thomas.

"If we were engaged in an objective discussion about the appropriate standards for judicial ethics, that would be perfectly appropriate. I don't believe that Democrats have any interest in an objective or fair discussion," said Sen. Ted Cruz, R-Texas, a member of the Judiciary panel. "This is all about a political smear job directed at Justice Thomas."

Supreme Court justices, like other federal judges, are required to file an annual financial disclosure report which asks them to list gifts they have received, but provides exemptions for hospitality from friends.

Ethics experts have offered conflicting views about whether Thomas was required to disclose the luxury trips funded by Crow. Thomas said in a statement that he was advised by colleagues that "this sort of personal hospitality from close personal friends, who did not have business before the Court, was not reportable." Thomas did not name the other justices or those in the judiciary with whom he had consulted.

Last month, the federal judiciary bolstered disclosure requirements for all judges, including the high court justices, although overnight stays at personal vacation homes owned by friends remain exempt from disclosure.

Durbin did not elaborate on the "steady stream" of ethical failings that he mentioned in his letter. Over the years, several justices have omitted travel from their annual disclosure reports, or failed to step aside from a case in which they held a financial interest.

When the court took up its first major case over the Affordable Care Act, Thomas and Kagan faced pressure to step aside from the case. Critics cited Kagan's role in the Obama administration when the law was enacted and the public advocacy of Thomas' wife, Ginni, against the Affordable Care Act.

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Associated Press writer Stephen Groves contributed.