The actress, who plays Emily Prentiss, was dropped from the CBS crime drama in June 2010, but returned for the latest season.
"I had another year on my contract that I didn't know about, so I had to come back!" she told TV Guide.
"I said, 'Hey, I kinda want an apology and maybe a raise'. And they were like, 'No, we'll sue you!' - the whole thing was, unfortunately, a mess. It was dumb."
AJ Cook (Jennifer 'JJ' Jareau) was also fired and later rehired alongside Brewster.
"They thought they would save money by getting rid of [me and AJ]," she explained. "And in the end, [they] got both of us back."
Brewster added that, despite past conflicts, she is keen to return to Criminal Minds for a potential eighth season.
"I love everyone here and it's just nice to have a job," she said. "[But] the only reason we have [season finale] cliffhangers is because of our contracts, so maybe [Prentiss will be in jeopardy this year]. I just kind of have to wait and see. They already fired me once!"
The Shield star Jay Karnes and Starship Troopers actress Dina Meyer will both appear in the 150th episode of Criminal Minds.
The show's anniversary instalment airs tonight at 9/8c on CBS.
> Criminal Minds exec denies Mandy Patinkin return
Watch a promo for the next Criminal Minds below: