29 May 1941,
Disney Studios’ workers started a strike where Walt Disney had just fired sixteen animators for syndication and defense of workers’ rights. They managed to paralyse the activity and Disney had to accept union recognition and wage increases. As a result, the other Hollywood animators also managed to improve their working conditions.
Source:
Tom Sito, Drawing the Line: The Untold Story of the Animation Unions from Bosko to Bart Simpson.