Republican Sen. John Curtis of Utah is calling on the Senate Judiciary Committee to investigate whether Donald Trump Jr. used his proximity to the presidency for financial benefit, after his recent wedding party was partially bankrolled by a Russian oligarch.

In a letter sent Tuesday, Curtis called on the committee to subpoena Trump Jr. over his business dealings, relationships with foreign individuals and entities, gifts or other benefits he has received and any instances in which his relationship to President Donald Trump, a Republican, “was invoked or understood to provide value.” Curtis called for the same scrutiny of Hunter Biden, the son of former President Joe Biden, a Democrat.

“The country should not have to accept one standard for the family of a Republican president and another for the family of a Democratic president,” Curtis wrote in the letter addressed to GOP Sen. Chuck Grassley of Iowa, chairman of the committee, and Sen. Dick Durbin of Illinois, the top Democrat on the committee.

The letter comes as a few Republicans have shown a growing willingness to criticize Trump after largely avoiding public breaks with the president during much of his second term. The unpopular war in Iran, high gas prices and mounting concerns about the GOP’s prospects in November’s midterm elections have brought increased scrutiny of the president from within his own party.