Michael Moore used some non-union crewmembers when union workers were available in the production of his latest film "Capitalism: A Love Story," a documentary that argues the capitalist system allows for greedy corporations to exploit working-class people.
"For all of the different jobs on the movie that could have used union labor, he used union labor, except for one job, the stagehands, represented by IATSE," said a labor source unauthorized to talk about Moore's decision not to hire members of The International Alliance of Theatrical Stage Employees.
In a statement issued to ABCNews.com, Moore's agent, Ari Emanuel, said the filmmaker wished the union included more documentary crew people -- but he did not deny that IATSE members were snubbed in favor of non-union employees.
"The sad fact is that documentary/verite theatrical films and the talented people who work on them are too often treated as second-class filmmakers, when they are among the most creative, talented and hardworking, and often produce our finest films," said Emanuel.
"Nothing would make Michael happier than for documentary filmmaking to get its due respect, and to have unions pursue the documentary film crews with the same energy they give to bringing feature crews into their membership and making it a viable option for them," he said.
"This is a Writer's Guild, Screen Actors Guild and Directors Guild film, as all of Michael's films are. He is a proud, dues-paying member of all three of these unions," said Emanuel.
Moore is the sole writer, director and professional actor credited in the film.
It was unclear exactly how many union or non-union employees worked on the film.
As a result of Moore's decision not to use IATSE workers, at least one other national union, the American Federation of Teachers has refused free tickets offered to them from Moore.
"Michael Moore and one of our sister unions, IATSE, are in discussions about concerns that union has. The AFT has decided against accepting free tickets until those issues are resolved," the teachers union said in a statement.
Both the teachers union and IATSE are members of the larger national labor organization, the AFL-CIO.
An internal AFT memo, obtained by ABCNews.com, added that the non-union workers hired for the film did not receive health insurance.
The organized labor source said Moore and IATSE were in talks about Moore's decision, but did not know why Moore had used union labor for some jobs and non-union employees for other jobs for which he could have employed union workers.
Moore has been screening his films to union audiences for the past two weeks and made a name for himself by championing autoworkers, like his father, in his first documentary, 1989's "Roger and Me."
Much of his newest film also focuses on union workers. The highlight of "Capitalism: A Love Story" concentrates on the successful six-day sit-in by 240 employees of Republic Windows and Doors in Chicago earlier this year.
Moore's film crew had the only cameras allowed inside the building during the sit-in, which culminated in a $1.35 million severance package from Bank of America. Moore screened the film to Republic employees last week.
After being criticized for using non-union extras in a 2000 music video he shot for the rock band Rage Against the Machine, Moore told the New York Post that he only learned they were hired after the video was completed.