A Republican senator demanded Monday that the Senate Judiciary Committee subpoena both first son Donald Trump Jr. and former first son Hunter Biden to investigate whether either or both men unlawfully used their proximity to the White House for money or other perks.

The request by Sen. John Curtis (R-Utah) is the first known call by a GOP legislator for a probe of the current president’s family and followed disclosures that Russian oligarch Umar Kremlev footed the bill for Donald Trump Jr.’s wedding festivities in the Bahamas earlier this year.

“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 to committee Chairman Chuck Grassley (R-Iowa) and ranking member Dick Durbin (D-Ill.). “Nor should congressional oversight begin and end when control of the White House changes hands.”

Curtis cited the younger Trump’s “active promotion of family-backed cryptocurrency ventures, his continued pursuit of international real estate deals involving direct meetings with foreign heads of state, and his reported investments in defense contracting” in calling for an investigation of “the use of presidential family relationships for private financial benefit, preferential treatment, or access by domestic and foreign interests.”

Trump Jr. and Hunter Biden would be asked to explain “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,” the lawmaker added.