Democratic Rep. Barbara Lee, here in Washington, DC, in 2022, filed paperwork Wednesday to run for US Senate in California. Credit: Al Drago / Bloomberg/Getty Images

(CNN) — Democratic Rep. Barbara Lee filed paperwork Wednesday with the Federal Election Commission to run for US Senate in California, setting up her entrance into a primary that’s shaping up to be competitive and crowded.

Lee hasn’t made an official announcement yet, and a spokeswoman told The Associated Press that Lee “is filing preparatory paperwork and her announcement will come before the end of the month.” Her filing comes one day after longtime Democratic Sen. Dianne Feinstein announced that she would not be seeking reelection next year.

When she does formally join the race, Lee will face off with two other prominent Democratic contenders who announced Senate bids earlier this year, Reps. Adam Schiff and Katie Porter. Under California’s primary system, all candidates run on the same ballot, with the top two vote-getters, regardless of party, advancing to the general election.

According to her most recent FEC filing, Lee had just $52,000 in cash on hand entering 2023, putting her at a disadvantage compared with her well-funded rivals. Schiff — who’s also been endorsed by former House Speaker Nancy Pelosi — had more than $20 million stockpiled at the end of the year, while Porter had more than $7.4 million.

Lee spoke of her plan to run for Senate with colleagues in the Congressional Black Caucus in January, around the time that Porter formally kicked off her bid for the seat Feinstein has held since 1992.

Porter’s campaign launch was followed weeks later by Schiff’s announcement that he would also run for Senate. Both entered the race before Feinstein had announced her reelection decision, under the presumption that the 89-year-old would retire at the end of her current term. Even Pelosi’s endorsement of Schiff was conditional — saying she would support him “if [Feinstein] decides not to run.”

A contest between Lee, Porter and Schiff would feature a contrast of resumes and identities. Lee, who represents an Oakland-area district, is currently serving her 13th full term in Congress, which she first entered after a 1998 special election. Her high-profile, lone vote against the 2001 Authorization for Use of Military Force, which authorized the war in Afghanistan and multiple subsequent overseas conflicts, earned her fierce criticism at the time.

If elected, Lee would also be just the third Black woman to serve in the US Senate, with none serving at present.

Porter was first elected to her Southern California seat in the 2018 midterms and has earned prominence and praise from progressives for her focused questioning of witnesses in House oversight hearings. She’s also been endorsed by her former law school professor, Democratic Sen. Elizabeth Warren of Massachusetts.

Schiff, a Los Angeles-area congressman, was first elected in 2000 and gained national attention during the Trump administration, serving in high-profile roles on the House Intelligence Committee and in both Trump impeachment proceedings.

Additional contenders could join the open Senate race in the nation’s largest state. Democratic Rep. Ro Khanna has publicly expressed interest in running. Other potential candidates include Health and Human Services Secretary Xavier Becerra — a former California attorney general — and San Francisco Mayor London Breed.

This story has been updated with additional information.