A Republican senator is calling for an investigation into the business dealings of Donald Trump Jr. and Hunter Biden following the revelation that a Russian oligarch paid for Trump Jr.’s post-wedding festivities in the Caribbean earlier this year.

Sen. John Curtis, R-Utah, sent a letter Monday to the leaders of the Senate Judiciary Committee, Chairman Chuck Grassley, R-Iowa, and ranking member Dick Durbin, D-Ill., requesting that the panel subpoena the president’s eldest son as well as former President Joe Biden’s son for testimony.

Curtis wants the two to provide information about “their past business dealings, relationships with foreign individuals and entities, gifts or other benefits they have received, and any instances in which their relationship to the President was invoked or understood to provide value.”

Curtis noted that Hunter Biden has “denied involving his father in his business dealings,” but the senator suggested he benefited from his father’s service in public office. He also expressed concern about Russian oligarch Umar Kremlev, who has ties to Russian President Vladimir Putin, paying for Trump Jr.’s post-wedding celebration in May.

“These reports raise legitimate questions about foreign access to members of a sitting president’s family and whether such relationships can create actual or perceived expectations of favorable treatment,” Curtis said. “They also may create expectations of a returned favor that would not be in the best interests of the American people or our allies, and could even create national security vulnerabilities.”

In a post on X Tuesday, Curtis criticized the president’s son. “A toaster is a wedding gift. A private-island party paid for by a Putin-connected oligarch is something else. Republicans nearly wore out the subpoena machine investigating Hunter Biden’s foreign relationships. We should not unplug it now. ‘Trust us’ was not enough then, and it is not enough now.”

A Judiciary Committee spokesperson said that the panel received Curtis’ letter and that hearing dates for the committee are extremely limited through the end of the year.

Durbin, however, voiced support for Curtis’ request.

“For the Committee to ignore this matter is to run the risk of being complicit in a coverup,” he said, noting that Hunter Biden had given a sworn deposition to Congress about allegations against him, while Trump Jr. has not.

Republicans have for years accused Hunter Biden of using his family’s connections to enrich himself through business deals in Ukraine and China, and several House committees investigated the allegations.

The Trump Organization, where Trump Jr. serves as executive vice president, and Hunter Biden didn’t immediately respond to requests for comment. NBC News also reached out to the White House.

Donald Trump Jr. and his wife Bettina Trump acknowledged Kremlev paid for their post-wedding celebration on a pair of Caribbean islands after ProPublica reported the connection.

In a joint Instagram post, they referred to the paid-for celebration as “an extraordinarily generous wedding gift from a friend, and something for which we were and remain incredibly grateful.”

They also said in the post that the vacation had been planned separately from their wedding, but when their nuptial plans changed, “we simply decided to get married before it.”

Last week, the president defended his son’s decision to accept the cash gift from Kremlev, but claimed that he has paid him back. “It’s totally allowed. But as I understand it, he paid him back. He didn’t want to have that, so I hear he paid him back.”

Some Republicans, especially in tight re-election races, are distancing themselves from Trump. Curtis, however, is currently serving his first term in the Senate and is not up for re-election until 2030.