Justice Clarence Thomas twice attended an annual donor summit organized by the conservative political network established by the billionaire industrialists Charles and David Koch, a spokeswoman for the group confirmed on Friday.
The justice’s presence at the summit was earlier reported by ProPublica.
The spokeswoman, Gretchen Reiter, said that Justice Thomas had only attended on those two occasions. He was invited first in 2008 to promote his memoir, “My Grandfather’s Son,” she said, and then to deliver remarks at a small dinner in 2018. She declined to comment on what Mr. Thomas discussed or who was in attendance.
The circumstances of Justice Thomas’s role at an elite donor event organized by a powerful right-wing organization renewed questions about his ethics practices, particularly given that the Koch network has brought several cases before the Supreme Court. One, in 2021, shielded charities in California from a requirement to report the identities of their major donors. In a dissenting opinion, members of the court’s liberal wing argued that the decision in the case had the potential to erode disclosure laws for political donations.
“The public must have faith that the justices’ decisions are informed by facts and law, and decades of decision-making, and are not influenced by a wealthy and powerful few,” Maya Wiley, the president of the Leadership Conference on Civil and Human Rights, said in a statement emailed on Friday.
Since disclosures about Justice Thomas’s decadeslong relationship with the billionaire real estate developer Harlan Crow shed light on a series of lavish gifts and travel that went unreported for years, scrutiny has intensified over the elite circles and powerful donors he moves among.
In a statement, the umbrella organization representing various elements of the Koch network, Stand Together, insisted that Justice Thomas’s attendance was unremarkable compared with other appearances by his colleagues on the court.
“There is a long tradition of public officials, including Supreme Court justices, sharing their experiences, ideas, and judicial philosophy with members of the public at dinners and other events,” the statement said.
In the statement, Stand Together also denied any improper influence over Justice Thomas’s vote in 2021, noting that it was supported in that case by other legal advocacy groups like the A.C.L.U. and the Human Rights Campaign.
A spokeswoman for the Supreme Court did not immediately respond to a request for comment.
The revelation is almost certain to renew calls for ethics laws covering the Supreme Court, as well as invite new scrutiny of a major administrative law case the court is considering in the coming term.
The case could pare back the regulatory power of administrative agencies, a long-held goal of the conservative legal movement. At issue is a 1984 precedent known as the Chevron doctrine, which requires courts to defer to administrative agencies’ interpretations of federal statutes. The Koch network’s lawyers and advocacy groups within the Koch network have challenged the validity of the statute on various fronts.
While Justice Thomas once came down in support of the precedent, in recent years he has signaled that he was open to reconsidering.
The Koch network has often turned to its annual summit as a prime venue to unveil big policy goals and notable political contributions. Attendees mingle with representatives of the Koch network, which includes the powerful libertarian conservative political advocacy group Americans for Prosperity Action.
In 2015, leaders at the summit announced an $889 million spending goal to influence legislation and races before the 2016 election — more money than Hillary Clinton’s or Donald J. Trump’s presidential campaigns ultimately spent themselves, according to fund-raising data compiled by Open Secrets, a nonprofit that tracks campaign finance data.
In 2018, Americans for Prosperity announced an initiative aimed at filling a future vacancy on the court with a justice in the same mold as Justice Neil M. Gorsuch, who was confirmed a year earlier. Months later, it followed up on that goal with a “six-figure direct mail and digital ad campaign” in support of Justice Brett Kavanaugh, who was nominated to replace outgoing Justice Anthony M. Kennedy and confirmed later that year.