The Senate Judiciary Committee is planning a Tuesday interview with a Russian-American lobbyist who attended a campaign meeting last year with President Donald Trump’s son, according to a person familiar with the interview.

The staff interview behind closed doors with Rinat Akhmetshin is part of the committee’s probe into Russian meddling in the 2016 election, as well as an ongoing investigation by Senate Judiciary Chairman Chuck Grassley into lax enforcement of the Foreign Agents Registration Act.

The person familiar with the meeting declined to be identified because it will not be publicly announced.

The panel’s investigation into Russian meddling has been stalled for weeks amid disputes between Republicans and Democrats. But Grassley has long said he wants to interview Akhmetshin about why he was not registered as a foreign agent.

Congressional investigators are probing the June 2016 meeting in Trump Tower with Donald Trump Jr., as is special counsel Robert Mueller. Akhmetshin was interviewed by the House intelligence panel Monday, and has also been interviewed by the Senate intelligence committee.

In emails ahead of the Trump Tower meeting, Trump Jr. enthusiastically agreed to the sit-down with Russian lawyer Natalia Veselnitskaya and others after he was promised dirt on his father’s rival, Democrat Hillary Clinton. Trump Jr. has since denied such material ever materialized.

Akhmetshin is a former military officer who has attracted congressional scrutiny over his political activities and has been shadowed by allegations of connections to Russian intelligence. Grassley said in a March letter that Akhmetshin has “reportedly admitted to being a ‘Soviet counterintelligence officer’ and has a long history of lobbying the U.S. government for pro-Russia matters.”

People who attended the 2016 Trump Tower meeting have made several appearances before congressional committees in recent months. The House intelligence committee earlier this month interviewed Ike Kaveladze, also known as Irakly Kaveladze, who was at the meeting as a representative of a Russian developer who once partnered with Trump to bring the Miss Universe pageant to Moscow.

Trump’s son-in-law, Jared Kushner, and his then-campaign chairman, Paul Manafort, were also in the meeting. Kushner met with both intelligence panels privately this summer and Manafort met with the Senate panel. Trump Jr. had a private interview with the Senate Judiciary Committee in September, but hasn’t met with the intelligence committees.

North Carolina Sen. Richard Burr, the Republican chairman of the Senate intelligence committee, has said he wants to wait to interview Trump Jr. until after committee staff has interviewed other participants in the meeting. Asked last week if the committee has interviewed all those other people, Burr said, “I think all but one.”

Also attending the Trump Tower meeting were publicist Rob Goldstone, who set it up with the promise of dirt on Clinton, and a translator.

Akhmetshin has said the Justice Department’s Foreign Agents Registration Act unit sent him a letter in April and told him, “it has come to our attention you should have filed for FARA.” He said he didn’t believe he needed to file. He has previously registered with Congress for the lobbying work, and he plans to raise this issue before Grassley’s committee.

“I think I have a legal right to tell my story,” he told The Associated Press earlier this year.

(AP)