WASHINGTON — A prominent conservative former federal judge joined a chorus of legal experts from across the political spectrum on Tuesday in calling on Congress to enact new ethical standards for Supreme Court justices, after a series of revelations about the justices’ undisclosed gifts, luxury travel and property deals.

The statement by Judge J. Michael Luttig, a retired appeals court judge revered by some conservatives, came as the Democratic-led Senate Judiciary Committee prepared to hold a hearing on Supreme Court ethics. Pressure has mounted among progressives for a stricter code of conduct for the justices, the nation’s highest judges, who are appointed to lifetime terms and are bound by few disclosure requirements.

Congress “indisputably has the power under the Constitution” to “enact laws prescribing the ethical standards applicable to the nonjudicial conduct and activities of the Supreme Court of the United States,” Judge Luttig said in a written statement presented to the Judiciary Committee.

The judge, who served on the U.S. Court of Appeals for the Fourth Circuit and was close to being nominated for the Supreme Court, was among several legal experts across the political spectrum who released testimony before a hearing scheduled for Tuesday in which they supported strengthening ethical rules at the court.

“It is time for Congress to accept its responsibility to establish an enforceable code of ethics for the Supreme Court, the only agency of our government without it,” Senator Richard J. Durbin, Democrat of Illinois and the committee’s chairman, said in a statement released in the days before the hearing.

During the hearing on Tuesday, lawmakers are expected to hear from five experts, including Jeremy Fogel, a former federal judge who directs the Berkeley Judicial Institute at the University of California, Berkeley; Kedric Payne, a vice president of the Campaign Legal Center, a campaign watchdog group; Amanda Frost, a law professor at the University of Virginia who specializes in legal ethics; Michael B. Mukasey, who served as attorney general in the George W. Bush administration from 2007 to 2009; and Thomas H. Dupree Jr., a partner at Gibson, Dunn & Crutcher.

Judge Luttig and Laurence Tribe, an emeritus professor of constitutional law at Harvard Law School who is a hero among some progressives, both released statements in support of ethical guidelines, but both declined to appear before the committee.

Mr. Tribe said he would leave it to others to say whether the current “crisis is sufficiently grave to call for particular legislative measures,” but that he saw the attempt to use legislation “to impose ethical norms in a binding way on the justices as eminently sensible.”

“I see such legislation as a necessary though probably not sufficient response to the current situation,” Mr. Tribe wrote.

Mr. Tribe added that he believed it would be “entirely prudent for Congress to enact norms in the form of rules binding on the justices if only as a prophylactic measure” to stop the court from being cast into “an ever darker shadow unhelpful to the esteem required for it to perform its function as a branch of government lacking both the sword and the purse and thus dependent on public respect for its integrity.”

Calls for the Supreme Court justices to be subject to an ethics code have grown in recent weeks after revelations about justices’ gifts, luxury travel and property deals highlighted how few reporting requirements are in place and how the justices are often left to police themselves.

ProPublica revealed that Justice Clarence Thomas had failed to disclose gifts, trips and a real estate deal with a wealthy Republican donor and real estate billionaire, Harlan Crow. The justice accepted flights on Mr. Crow’s private jet to Bohemian Grove, an exclusive retreat in Northern California; an island vacation aboard his superyacht in Indonesia; and trips to Mr. Crow’s 105-acre lakeside resort in the Adirondack Mountains. None appeared on the justice’s financial disclosure forms.

The justice also failed to disclose a real estate deal with Mr. Crow in which the billionaire bought properties from the justice and his family, including Justice Thomas’s mother’s home in Savannah, Ga. Mr. Crow paid $133,363 to the justice and his family for the property, according to records filed at Chatham County courthouse dated Oct. 15, 2014. Justice Thomas’s mother, Leola Williams, still lives in the home.

Justice Neil M. Gorsuch sold property to the chief executive of a major law firm that often has business before the court and did not disclose the identity of the buyer, as was first reported by Politico. Experts said it underscored the need for reform.

Mr. Durbin sought the testimony of Chief Justice John G. Roberts Jr., but the chief justice released a letter last week declining an invitation to testify, citing separation of powers issues. In a statement that accompanied his letter, all nine justices signed onto a “statement of ethics principles and practices” laying out the guidelines that they use to govern their behavior and disclosures.

They said that they follow the same general ethical standards that apply to other federal judges. But they also said they may be limited in what to disclose because of security concerns. In fact, financial disclosures are not filed immediately and must be submitted each year in May.

There has been discussion in recent years that the justices adopt rules governing their behavior.

The chief justice wrote in 2011 in his year-end report that the justices did not need to be bound by the Code of Conduct for United States Judges, which applies to other federal judges.

“All members of the court do in fact consult the code of conduct in assessing their ethical obligations,” he wrote, adding: “Every justice seeks to follow high ethical standards, and the Judicial Conference’s code of conduct provides a current and uniform source of guidance designed with specific reference to the needs and obligations of the federal judiciary.”

Justice Elena Kagan told a House committee in 2019 that Chief Justice Roberts was “studying the question of whether to have a code of judicial conduct that’s applicable only to the United States Supreme Court.”

The justices have not announced such a code of conduct.

“In light of the Supreme Court’s failure to take action, Congress must step in to protect the justices from themselves,” Ms. Frost, the University of Virginia professor, said in prepared testimony.