An international group of actors’ unions, including SAG, has warned members not to work on “The Hobbit” because of failed efforts to organize the film’s New Zealand production — a move Peter Jackson disparages as a “power grab.”

Members were advised [1] in an alert sent over the weekend “not to accept work on this non-union production” of the MGM blockbuster-to-be, which is still awaiting the official greenlight from financially troubled MGM before shooting — tentatively scheduled for next year — can begin.

Guilds involved include SAG, AFTRA and several international unions. The New Zealand unit of an Australian union had made attempts to organize the film, according to the alert.

But Jackson fired back in a statement Sunday, saying the Kiwi organization represents a very tiny percentage of actors there, and is leveraging his production to gain membership.

Actors guilds are known to issue member alerts of this sort from time to time, but it is extremely rare for a major studio franchise film to be involved.

Here’s the full text of the alert:

The makers of feature film The Hobbit – to be shot in New Zealand next year – have refused to engage performers on union-negotiated agreements.

Members of Canadian Actors Equity, US Actors Equity, the Screen Actors Guild, UK Actors Equity, the American Federation of Television and Radio Artists, the Media, Entertainment & Arts Alliance (Australia) and the Alliance of Canadian Cinema, Television and Radio Artists are advised not to accept work on this non-union production.

If you are contacted to be engaged on The Hobbit please notify your union immediately.