Disney said ByteDance had pre-packaged Seedance with a pirated library of copyrighted characters from franchises including Star Wars and Marvel, portraying them as if they were public-domain clip art, a source familiar with the matter told Reuters.
The letter alleges Seedance is reproducing, distributing and creating derivative works featuring Spider-Man, Darth Vader, and other characters, the person added.
ByteDance will strengthen safeguards on its Seedance 2.0 AI video tool to prevent the unauthorised use of copyrighted characters and celebrity likenesses, the Chinese firm told the BBC on Sunday.
ByteDance did not immediately respond to Reuters' request for comment.
Online news outlet Axios was the first to report on Disney's move.
Paramount Skydance has also sent a cease-and-desist letter to ByteDance, accusing the Chinese firm of engaging in "blatant infringement" of its intellectual property, Variety reported at the weekend.
Videos generated by Seedance 2.0, which was released last week, have gone viral in China including one of Tom Cruise and Brad Pitt in a fight.
The AI model has been compared to DeepSeek and has been praised for its ability to produce cinematic storylines with just a few prompts.
Disney has taken similar actions against Character.AI, demanding the startup immediately stop the unauthorised use of its copyrighted characters.
In December, Disney signed a licensing deal with OpenAI, letting the startup use characters from Star Wars, Pixar and Marvel franchises in its Sora video generator.
