It could have meant hundreds of carpenters, painters and stage hands walking out on the set of Potter 3, which could have seriously delayed the movie.
New faces
But now a deal's been struck between Potter film-makers, Warner Brothers, and the workers' union.
Filming of the latest Potter movie started at Leavesden Studios in Hertfordshire, and Shepperton Studios in London, in February.
Most of the old faves are back in it, as well as some new faces too, like British actor Gary Oldman, who'll be playing Sirius Black, and Timothy Spall, who'll playing Peter Pettigrew.
Hear Story
All our Potter interviews
Choose your Potter board
