Sen. Dianne Feinstein wants Attorney General Jeff Sessions to testify before the Senate Judiciary Committee in either August or September about his contacts with Russian officials.

In a Monday letter, the California Democrat said it was a "serious matter" that Sessions had "substantive" conversations with Russian ambassador Sergey Kislyak while he was an advisor to the Trump campaign in 2016, an event the Washington Post reported.

During his confirmation hearing in January, Sessions did not disclose conversations that he had with the Russian ambassador. But since those conversations came to light, he has amended his confirmation testimony and recused himself from the Justice Department's investigation into Russian meddling in the 2016 presidential election. Sessions also testified before the Senate Intelligence Committee and denied there was a link between him and the Russians during the campaign.

"As the head of the Justice Department, he holds a unique position of trust within our government," Feinstein wrote. "It would be a grave breach of trust if the Attorney General gave false or misleading testimony to this committee."

Feinstein said that despite "repeated" requests by herself and other committee members, Sessions "has still not been invited to testify before the committee," which she said has "primary jurisdiction" into oversight of the Justice Department.