Democratic members of the Senate Judiciary Committee have given Harlan Crow, a billionaire Republican donor, until May 22 to provide the panel with a full accounting of gifts and other valuable benefits provided to Justice Clarence Thomas or other members of the Supreme Court.

In a letter sent on Monday, Senator Richard J. Durbin of Illinois, the chairman of the committee, led fellow Democrats in pressing Mr. Crow for documentation of gifts and travel provided to justices as well as any real estate transactions involving members of the court. The letter sought information on benefits valued above $415 — the threshold for reporting such transactions for federal judges — including admission to private clubs.

The committee’s action followed reports by ProPublica and others that Mr. Crow provided luxury travel for Justice Thomas, purchased real estate from him and paid private school tuition for his relative — arrangements that were not reported on the justice’s financial disclosures.

Members of the Supreme Court have said they are not bound by the disclosure rules applied to the rest of the federal judiciary but that they do voluntarily abide by them.

The disclosures of the financial ties between Mr. Crow and Justice Thomas have intensified calls for tighter disclosure and ethics rules on the court, though Chief Justice John G. Roberts Jr. has said the court is capable of policing itself. He refused to take part in a recent Judiciary Committee hearing on possible new ethics rules, citing separation of powers issues.

In the letter, the Democrats said the information they were seeking from Mr. Crow would help the committee correct shortcomings in the court’s current ethics and disclosure framework.

“We’re seeking information on whether individuals with interests before the Supreme Court were able to gain access to Justices through gifts, lodging, and travel from Harlan Crow and his companies,” Mr. Durbin said in a tweet on Tuesday. “If the Supreme Court won’t implement ethics reform itself, @JudiciaryDems will.”

Justice Thomas has said he did not believe he was obligated to disclose his travel given his friendship with Mr. Crow and an exemption from disclosure requirements for personal hospitality.

Mr. Durbin has so far held back from threatening subpoenas to obtain information or compel testimony from the justices or others. It is unclear whether he would have the votes to issue them, given the long-running absence for medical reasons of Senator Dianne Feinstein, Democrat of California, a senior member of the panel. Ms. Feinstein signed the new letter to Mr. Crow, but her unavailability could prevent the committee’s Democrats from winning approval of a subpoena, given Republican opposition.

The Senate Finance Committee is seeking similar information from Mr. Crow. In a letter after the initial reports of Mr. Crow’s undisclosed expenditures on behalf of Justice Thomas, Senator Ron Wyden, Democrat of Oregon and the chairman of that panel, asked Mr. Crow for a similar listing of any benefits provided to the justice, saying the panel wanted to assess whether tax laws had been followed.

“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,” Mr. Wyden’s letter said. He said that if Mr. Crow failed to comply voluntarily with his request for documentation, he would “explore using other tools at the committee’s disposal to obtain this critical information.”

Besides Mr. Crow himself, the Judiciary Committee Democrats also sought information from the business entities affiliated with Mr. Crow that were responsible for accommodating Justice Thomas at an Adirondacks resort and on a private jet and yacht. Letters to those companies asked for the itineraries of Justice Thomas or any other member of the Supreme Court, as well as the identities of others traveling with them.

“The appearance of special access to the justices — that is not available to all Americans — is corrosive to the legitimacy of the court because, at minimum, it creates an appearance of undue influence that undermines the public’s trust in the court’s impartiality,” the Judiciary Committee Democrats wrote in explaining their request.