Though deals have already been made with The Simpsons writers and producers, the show's key cast members - Dan Castellaneta, Julie Kavner, Nancy Cartwright, Yeardley Smith, Hank Azaria and Harry Shearer - have yet to sign up for season 20.
The cast members reportedly make in the region of $360,000 per episode but are looking to bump the figure closer to the $500,000 mark.
The Simpsons voice cast has been involved in contract disputes with network Fox in the past. When they asked for a significant raise in 1998, the network hired casting directors to find potential replacements. Six years later, production halted when the cast failed to show up for two table reads. At the time they were looking to increase their $125,000-per-episode salary.
Fox has already put production on hold for season 20 and is likely to turn around 20 episodes this season as opposed to the usual 22. That figure could be reduced further the longer it takes to agree on new contracts for the voice cast.