EXCLUSIVE: After three days of intense bargaining, negotiations for a new SAG-AFTRA video game contract have deadlocked and a federal mediator will be called in this afternoon in an attempt to head off a threatened strike.

The main issue is the union’s demand that performers receive an additional full-scale payment for each 500,000 units sold, up to a maximum of four secondary payments if the game sells 2 million units. “The No. 1 thing is residuals,” said an actor who has worked on dozens of games. “This is the only billion-dollar industry where actors are paid no residuals.”

SAG-AFTRA’s board of directors voted unanimously Sunday to strike the video game companies if a deal isn’t reached by midnight Thursday night.