Justice Clarence Thomas never disclosed three trips aboard the private jet of the Texas billionaire Harlan Crow, according to documents obtained by the Senate Judiciary Committee released on Thursday.

The documents, obtained by Democrats on the panel, list three visits that have not previously been reported: one to a city in Montana, near Glacier National Park, in 2017; another to his hometown, Savannah, Ga., in March 2019; and another to Northern California in 2021.

The purpose of each trip was not immediately clear, nor was the reason for their omission on the justice’s disclosure forms. However, all of the flights involve short stays: two were round trips that did not include an overnight stay.

The revelation underlined the extent to which Justice Thomas has relied on the generosity of his friends over the years and the consistency with which he declined to report those ties.

Justice Thomas has said that he had been advised he did not need to disclose gifts of personal hospitality from friends who did not have cases before the Supreme Court.

The announcement is all but certain to fuel the fight over greater transparency at the Supreme Court. Lawmakers’ efforts to require that justices be held to ethics standards similar to those for the executive and legislative branches have faltered. And even as the court, under immense public scrutiny, announced its first ethics code in the fall, experts immediately pointed out its lack of an enforcement mechanism or penalties should a justice have violated it.

The revealing of the trips “makes it crystal clear that the highest court needs an enforceable code of conduct, because its members continue to choose not to meet the moment,” Senator Richard J. Durbin, Democrat of Illinois and the chairman of the committee, said in a statement.

Justice Thomas did not immediately respond to a request for comment. His lawyer, Elliot S. Berke, did not respond to questions about details of the trips, but defended the trips in a statement.

The information, supplied to lawmakers by Mr. Crow, “fell under the ‘personal hospitality exemption’ and was not required to be disclosed by Justice Thomas,” Mr. Berke said.

Mr. Berke was referring to an exception to federal disclosure requirements that underwent a rule change by the Administrative Office of U.S. Courts in March last year. The change required the justices to disclose more of their activities, including some free trips, air travel and other types of gifts. All three trips happened before that rule change.

Mr. Berke said that, since the rule change, “Justice Thomas has fully complied with the new disclosure requirement.”

A spokesman for Mr. Crow, Michael Zona, said in a statement that Mr. Crow had agreed to cooperate with the committee, furnishing “information responsive to its requests going back seven years.”

The first trip, from May 7 to 9, 2017, involved a private jet flight from St. Louis, Mo., to Kalispell, Mont., and onto Dallas, Texas.

Justice Thomas delivered remarks at the Bar Association of Metropolitan St. Louis on Friday, May 5, 2017, but it is not clear what he was doing in Montana. Kalispell, a city of roughly 29,000 in the state’s northwest, is known as a gateway to Glacier National Park, a haven for fly fishing and hiking. The reasons for his stop in Dallas, where Mr. Crow lives, are unclear.

The second trip took place on March 23, 2019. It was a single-day, round-trip to Savannah, Ga., where he grew up. His mother and several relatives remain in the area.

The third trip was also a single-day excursion, a round-trip flight on June 29, 2021, from Washington, to San Jose, Calif. The court issued at least three opinions that day, according to the Supreme Court website, but it was during the Covid-19 crisis when the justices were allowed to work remotely, meaning they did not have to appear in person in the courtroom.

According to his most recent financial disclosure report, which was released last week, Justice Thomas amended previous filings to add 2019 vacations with Mr. Crow to Bali, Indonesia, and Bohemian Grove, a secretive, all-male retreat in Northern California. Justice Thomas did not report any private jet flights or travel from benefactors for 2023, the year covered by the most recent disclosure.

He listed one gift: a pair of photo albums worth $2,000 from Terrence and Barbara Giroux. Mr. Giroux is the departing executive director of the Horatio Alger Association of Distinguished Americans, an exclusive group that includes figures at some of the highest echelons of society.