The actor, who played Elle Woods in the hit comedy movie, teased a virtual reunion for her co-stars Jennifer Coolidge, Luke Wilson, Ali Larter, Holland Taylor, Selma Blair, Jessica Cauffiel and Alanna Ubach.
Posting on Instagram, Reese revealed that fans will be able to watch their reunion on YouTube on Tuesday.
“Ohmigod you guys!! It’s a Legally Blonde Reunion,” she wrote, sharing a preview of the video. “We laughed, we cried and we may or may not have done the bend & snap for old times sake!
“For the first time in 20 years, join me and the #LegallyBlonde cast tomorrow at 3:15PM PST on the @hellosunshine YouTube channel! PS: Don’t you want to see if Elle & Warner finally make up?”
The cast are raising funds for the World Central Kitchen with their reunion, which is a non-profit organisation devoted to providing meals in the wake of natural disasters.
Legally Blonde, which followed a sorority girl who attempts to win back her law student ex-boyfriend by getting a law degree, was released in 2001 and became a sleeper hit for the MGM studio.
Reese reprised her lead role as Elle Woods in a 2003 sequel, with many of the original cast also returning.
Earlier this year, it was reported there had been discussions about a third instalment of the franchise.