Sen. Dianne Feinstein (D-CA) has turned over a letter concerning Supreme Court nominee Brett Kavanaugh to the FBI.

“I have received information from an individual concerning the nomination of Brett Kavanaugh to the Supreme Court,” Feinstein said in a statement Thursday. “That individual strongly requested confidentiality, declined to come forward or press the matter further, and I have honored that decision. I have, however, referred the matter to federal investigative authorities.”

An FBI spokesperson declined to answer questions about the letter, saying only:

“Upon receipt of the information on the night of September 12, we included it as part of Judge Kavanaugh’s background file, as per the standard process.“

According to a BuzzFeed News report, the letter was first received by Rep. Anna Eshoo (D-CA), who turned it over to Sen. Feinstein.

According to a Huffington Post report, sources say that the matter involves a decades-old episode between Kavanaugh and a woman. Senate Judiciary Committee Chairman Chuck Grassley (R-IA) told reporters that he is aware of the situation, but declined to comment until he saw the letter itself.

The White House released a statement on the letter Thursday afternoon, noting that the “Federal Bureau of Investigation has thoroughly and repeatedly vetted Judge Kavanaugh, dating back to 1993, for some of the most highly sensitive roles.”

“Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new ‘information’ about him,” the White House said.