The chairman of the Senate Judiciary Committee said he is sending a letter to Donald Trump Jr to ask him to testify.
Senator Chuck Grassley said he would subpoena the president's eldest son if necessary.
The Iowa Republican says he wants Mr Trump Jr to appear "pretty soon", and it could be as early as next week.
Mr Trump Jr released emails this week from 2016 in which he appeared eager to accept information from the Russian government that could have damaged Hillary Clinton's campaign.
The panel is investigating Russian meddling in the US election.
Mr Grassley would not say what he wants to hear from the president's eldest son, but said members aren't restricted "from asking anything they want to ask".