The Association of Talent Agents, which represents major Hollywood agencies, said that the suit “confirms that the W.G.A.’s leadership is on a predetermined path to chaos.”

“Knowing that it could take months or even years for this litigation to be resolved, W.G.A. leaders are unnecessarily forcing their members and our industry into long-term uncertainty,” said Karen Stuart, the executive director of the A.T.A. “While the legal process runs its course, we strongly believe that in the interim it remains in the best interests of writers to be represented by licensed talent agencies.”

The agencies have been steadfast in arguing that packaging fees benefit both writers and their representatives. The main interest of both camps — the creation of hit shows — is well served by the current arrangement, they say. The agencies have also said that, with the growing power of Netflix and other streaming services, writers need agents to defend their interests more than ever.

In addition to the unions, eight accomplished writers signed onto the lawsuit, including Meredith Stiehm, the creator of the CBS series “Cold Case,” and David Simon, the creator of “The Wire.”

Mr. Simon, in a widely shared entry he posted on his personal blog last month, wrote of packaging: “It is theft. It is fraud. In the hands of the right U.S. attorney, it might even be prima facie evidence of decades of racketeering.”

In its suit, the W.G.A. argues that packaging fees violate California fiduciary duty law, saying that talent agents are required by law to be loyal to their clients and without conflict of interest. The filed complaint also argues that packaging fees violate California’s Unfair Competition Law, and says they violate a federal statue of the Labor-Management Relations Act, an anti-kickback provision of the Taft-Hartley Act.

Members of the guild and their opponents at the agencies have shown united fronts, with only a few exceptions. Jon Robin Baitz, a writer working on a new Amazon series starring Julia Roberts, said in a letter to the W.G.A. that he would not cut ties with his representatives at the Creative Artists Agency.