Rep. Barbara Lee filed federal paperwork on Wednesday to enter the race for the California Senate seat held by Dianne Feinstein. 

Although Lee has not made a formal announcement yet, her entry is widely expected.

Lee filed to create a Senate fundraising committee one day after Feinstein, 89, announced that she would step down from her position after her term ends. 

Katie Merrill, a spokesperson for Lee, told The Associated Press that Lee is "filing preparatory paperwork and her announcement will come before the end of the month."

A LOOK BACK AT SOME OF SEN. DIANNE FEINSTEIN'S MOST TROUBLESOME MOMENTS IN THE SENATE

Rep. Barbara Lee

Rep. Barbara Lee, D-Calif., attends a news conference with the Pro-Choice Caucus on the reintroduction of the "Equal Access to Abortion Coverage in Health Insurance (EACH) Act, outside the U.S. Capitol on Jan. 26, 2023.  ((Tom Williams/CQ-Roll Call, Inc via Getty Images))

Lee would join a growing field of candidates, including fellow Democratic Reps. Katie Porter and Adam Schiff, in the contest to fill Feinstein's seat.

Lee said in a statement on Wednesday that it has been an "immense honor" to work alongside Feinstein in California, and highlighted Feinstein's service in Congress. 

California Sen. Dianne Feinstein will not seek re-election

FILE - Sen. Dianne Feinstein, D-Calif., arrives for the Senate Democratic Caucus leadership election at the Capitol in Washington, Thursday, Dec. 8, 2022.  (AP Photo/J. Scott Applewhite, File)

"I'd like to congratulate Senator Feinstein on her historic, trailblazing career and echo the gratitude of her constituents in our beautiful state for her service," Lee said.

DIANNE FEINSTEIN ANNOUNCES SHE WILL NOT SEEK RE-ELECTION IN 2024

Rep. Barbara Lee in Washington, D.C.

Rep. Barbara Lee (D-CA) arrives for votes at the U.S. Capitol on Jan. 12, 2023, in Washington, D.C.  ((Kent Nishimura / Los Angeles Times via Getty Images))

The 76-year-old is the highest-ranking Black woman appointed to the House Democratic leadership, serving as co-chair of the Policy and Steering Committee.

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Lee is perhaps best known for being the only member of Congress to vote against the authorization for the use of military force after the terrorist attacks of Sept. 11, 2001.

The Associated Press contributed to this report.