Barbara Kopple (Harlan County, U.S.A.) and Cecilia Peck document the furor that erupted in the U.S. after Dixie Chicks singer Natalie Maines, performing in London shortly before the invasion of Iraq, made an onstage crack about President Bush. The movie endorses the liberal conception of the Chicks as free-speech heroes, which doesn’t quite wash: Maines shot her mouth off to a receptive overseas crowd, then issued an apology as soon as the backlash began back home. But unfettered access to the band’s strategy sessions with their manager and publicist yields a fascinating story nonetheless, as a corporate blacklist forces the country-radio honeys to reinvent themselves as rock-radio rebels and in the process find something deeper in their music. R, 93 min. a Pipers Alley, River East 21.