Barton's character, Marissa Cooper, was killed in the show's season finale last week.
Schwartz claims killing off the character was a creative decision and had nothing to do with the actress, saying, "She was a complete professional."
However, a source tells Us Weekly, "This was not a mutual decision."
The 20-year-old star had hinted she wanted to focus on her film career, but co-star Peter Gallagher disagrees.
Gallagher says, "You can't say (whether) that's true or not, but I think she was pretty happy on the show."
Sources close to the program claim Barton's character was killed to raise the profile of the series, which has recently struggled in the ratings.
The sources adds, "Everybody's talking about The O.C. again, and that's exactly what they want."
Article Copyright World Entertainment News Network All Rights Reserved.