Lord of the Rings director Peter Jackson is expected to take over the helm of the two-part prequel The Hobbit. (Chris Park/Associated Press)

Seven actors unions from around the world have advised their members not to take roles in The Hobbit movies, the two-part prequel to the Lord of the Rings trilogy.

Unions in Canada, Australia, the U.S. and U.K. say producers of the big-budget movie have refused to negotiate with them.

Lord of the Rings director Peter Jackson is the executive producer of the prequel, which will be split into two films. New Line and MGM studios are financing the film and have yet to comment on the matter.

Under the umbrella of the International Federation of Actors or FIA, the seven unions say performers with the production, being shot in New Zealand where Jackson lives, have "struggled on non-union contracts" for years.

That means there are "no minimum guarantees of wages or working conditions," no residuals for future broadcasts and no cancellation payments, the unions said in a statement.

Canadian organizations affiliated with the federation include ACTRA (Alliance of Canadian Cinema, Television and Radio Artists), CAEA (Canadian Actors' Equity Association) and UDA (Union des Artistes).

The action is the latest in a series of snags that have hit the production, which is expected to start filming in 2011.

Due to financial problems at New Line and MGM, the film is still stuck in development

Mexican director Guillermo Del Toro jumped out of the director's chair after spending a few years on the project, saying the delays were going on too long and he had several other films to do.

Jackson, who won a best director Oscar for his work on Lord of the Rings: The Return of the King, is supposed to take over but this has yet to be announced.