The Entertainment Software Association, the trade association which represents US game publishers, is losing Activision and Vivendi as member companies.

UPDATE: We've just received confirmation from the ESA. Rich Taylor, ESA Senior Vice President of Communications and Research, issued the following statement:
 

While the Entertainment Software Association remains the preeminent voice for U.S. computer and video game publishers, we can confirm that Activision and Vivendi Games opted to discontinue their membership.

The ESA remains dedicated to advancing our industry’s objectives such as protecting intellectual property, preserving First Amendment rights, and fostering a beneficial environment for the entire industry. Our high level of service and value to members and the larger industry remains unchanged.

We began working on this story this morning after reading online reports that Activision would not be exhibiting at E3 in July. Beyond that information, GamePolitics observed that the ESA's new website lists neither Activision or Vivendi as member companies.

The two game publishers, of course, are in the process of merging into Activision Blizzard. The reason for their decision to leave the ESA remains unclear at this point. Also unclear is whether any additional game publishers may defect from ESA member ranks.

The loss of two of its larger member firms will likely have a significant impact on the ESA's revenue base. In addition to its own operations, the ESA funds E3, the Video Game Voters Network, the Academy of Interactive Arts & Sciences and the D.I.C.E. Summit. Any or all of those entities could feel the repercussions from the ESA's loss of member revenues.

UPDATE 2: We've got comment from Activision now:
 

After careful consideration, Activision has decided not to renew its ESA membership for business reasons and will not be participating in any official E3 activities.  We appreciate the work that the ESA has done over the years in promoting the interactive entertainment industry with state and federal governments and wish the ESA best of luck with the show.

UPDATE 3: Kotaku is reporting that four more publishers (NCSoft, Codemasters, id and Her Entertainment) won't participate in E3, although they are not dropping out of the ESA). Kotaku also has quotes from Wedbush-Morgan's Michael Pachter, who blames ESA president Mike Gallagher for the current issues with the publishers:
 

Lowenstein was a very savvy industry veteran who paid attention to the goings-on in the industry and cared what the community had to say. The new person... whose name completely escapes me because I've never met him or heard from him, is far less knowledgeable and sophisticated about this industry than Doug was and is going to make some rookie mistakes.

Doug used to be a very visible spokesperson in congress... when you'd get these [things like] Barack Obama saying videogames are corrupting our youth or MADD saying that Take-Two should pull GTA off the shelves, you would hear Lowenstein immediately shoot back. I would guess that Activision doesn't perceive the same value from the ESA as they did under Doug's leadership. I criticize [Gallagher's] lack of drive to learn about the industry.