(NewsNation) — After reporting from investigative news outlet ProPublica revealed undisclosed financial gifts given to Supreme Court Justice Samuel Alito from a billionaire, Alito responded with an op-ed in the Wall Street Journal denying he was out of compliance with ethical standards.

ProPublica reported on a fishing trip Alito took as a gift from Paul Singer and failed to declare on a financial disclosure form. Singer, who made his money from hedge funds, has appeared before the Supreme Court multiple times and Alito also did not recuse himself in any of those cases.

In his op-ed, Alito argued that he was not required to recuse himself or to declare the vacation he was given based on the ethical standards of the court.

Alito said his relationship with Singer was not significant enough to require him to recuse himself to avoid the appearance of impropriety. He also indicated he was not necessarily aware of Singer’s involvement in some of the cases that came before the court, because Singer was not a listed party in those cases, which involved corporations Singer had connections to.

“The entities that ProPublica claims are connected to Mr. Singer all appear to be either limited liability corporations or limited liability partnerships. It would be utterly impossible for my staff or any other Supreme Court employees to search filings with the SEC or other government bodies to find the names of all individuals with a financial interest in every such entity,” Alito wrote.

Alito also defended his failure to report the vacations, on the grounds that accommodations and transportation for social events were not reportable gifts.

“The flight to Alaska was the only occasion when I have accepted transportation for a purely social event, and in doing so I followed what I understood to be standard practice,” he wrote.

Alito is not the only justice that ProPublica found to have undisclosed donations. It also reported on luxury vacations Justice Clarence Thomas received from a wealthy donor.