WASHINGTON — Sen. Dianne Feinstein, D-Calif., confirmed Thursday that she had referred information about Supreme Court nominee Brett Kavanaugh to "federal investigative authorities."

“I have received information from an individual concerning the nomination of Brett Kavanaugh to the Supreme Court. 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,” said Feinstein, the top Democrat on the Senate Judiciary Committee, which is scheduled to vote on Kavanaugh’s nomination next week.

Senate Judiciary Committee Democrats met on Wednesday night to discuss a vague sexual misconduct allegation against Kavanaugh dating back to his high school days, two sources familiar with the matter told NBC News.

The information came from Rep. Anna Eschoo, D-Calif., whose office pointed NBC News to a statement released last week that they had "a confidentiality policy regarding constituent casework" that precluded the release of any further details. The existence of the letter was first reported by online publication The Intercept.

Two sources told NBC News the allegation was sexual in nature, but both said the letter writer was not specific in describing Kavanaugh's alleged behavior. One source told NBC News the conduct described could allege sexual assault, but said it could also be a lesser allegation — and added the individual making the allegation would have to be more specific with law enforcement officials for any investigation to be able to move forward.

The FBI has said it is not opening a criminal investigation into the matter.

George Hartmann, a spokesman for Sen. Chuck Grassley, R-Iowa, chairman of the Judiciary Committee, said Thursday that the senator is aware of Feinstein's referral.

"At this time, he has not seen the letter in question, and is respecting the request for confidentiality," Hartmann said. "There's no plan to change the committee’s consideration of Judge Kavanaugh's nomination."

Feinstein had been in possession of the letter for some period of time, two sources said, but the matter was not referred to the FBI until after the Democrats met on Wednesday evening. The meeting was called because members of the committee had heard rumors of the letter's existence from reporters, one source told NBC News.

White House spokesperson Kerri Kupec said Thursday that Feinstein should have raised the information earlier in the nomination process.

"Not until the eve of his confirmation has Sen. Feinstein or anyone raised the specter of new ‘information’ about him," Kupec said, accusing Democrats of an "11th-hour attempt to delay" Kavanaugh a seat on the high court. "Throughout 25 years of public service, the Federal Bureau of Investigation has thoroughly and repeatedly vetted Judge Kavanaugh, dating back to 1993, for some of the most highly sensitive roles."

The controversy comes after a marathon series of confirmation hearings for Kavanaugh's nomination last week in which he testified for two days before the Judiciary panel. The committee was originally scheduled to vote on his nomination Thursday morning, though it has now been delayed until next week on Sept. 20.