"Distributors Weinstein Co are "exploring legal action" because NBC rejected ads for their film about the Dixie Chicks' criticism of George Bush.
The film shows the bad public reaction after the band's Natalie Maines said she was "ashamed" Bush came from Texas.
NBC said it was following its "policy of not broadcasting ads that deal with issues of public controversy".
The ad includes footage of the Iraq War and background on Maines' onstage comments in London.
Radio stations later refused to play the band's songs, while their albums were destroyed in the street.
The documentary Shut Up and Sing follows the country music group from the gig in 2003 in which Maines made her comment to the release of their latest album, after which they began to tour again.
The local channels of all the major US broadcasters have been showing the commercials.
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