(AP) — The Writers Guild of America is suing Hollywood’s four biggest talent agencies in the latest and boldest move in an increasingly bitter fight between the two sides.

The suit filed Wednesday in Los Angeles Superior Court claims that agents’ use of so-called packaging fees is illegal under California law because they pose a conflict of interest in representing writers.

Packaging fees mean agents combine elements of a television series, including writers, scripts or actors, and sell them directly to studios as a unit rather than taking commission from each. It can mean massive payouts for agents from successful shows, sometimes more than those who directly work on them receive.

The common practice has fueled increasingly heated negotiations between agencies and the guild. Numerous writers have fired their agents.

The agencies said they would have comment later Wednesday.