Sen. Dianne Feinstein Dianne Emiel FeinsteinBiden leads Trump by 12 points among Catholic voters: poll Names to watch as Trump picks Ginsburg replacement on Supreme Court McConnell says Trump nominee to replace Ginsburg will get Senate vote MORE (D-Calif.), the ranking member of the Senate Judiciary Committee, said the panel intends to send former Trump campaign manager Paul Manafort a subpoena, CNN reported Wednesday.

Feinstein said she struck a deal on the key areas of interest in their probe with the committee chairman, Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyGardner signals support for taking up Supreme Court nominee this year Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee McConnell digs in on vow to fill Ginsburg's Supreme Court seat MORE (R-Iowa).

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"We've agreed on a subpoena for Manafort," Feinstein told the news outlet.

Their investigation is looking into Russia's attempts to interfere in the 2016 election, with the leaders deciding to pursue details of Manafort's ties to the Kremlin.

Manafort agreed in July to turn over documents related to the Foreign Agents Registration Act after facing scrutiny for failing to properly register during the time he was working with company that had ties to Ukraine.

Despite this, Grassley has reportedly grown frustrated with Manafort’s lawyers, who he believes have been uncooperative.

Issuing a subpoena aims to add pressure and prompt the former campaign chairman to appear at a hearing in front of the Judiciary Committee.

A spokesperson for Grassley confirmed that several general agreements had been made in principle on the matter, though details were still being ironed out. The spokesperson declined to elaborate further.

A Manafort spokesman declined CNN’s request for comment.

The Senate committee is also reportedly weighing whether to similarly issue a subpoena for Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE Jr., who held a controversial meeting with a Russian lawyer last year at Trump Tower in which he sought damaging information about Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE.

Manafort is also a person of interest in special counsel Robert Mueller's probe, and an investigative team raided his house in late July to seize materials from his residence.