In 'Sing,' a trio whistles Dixie

You could say that "Dixie Chicks: Shut Up & Sing" is a terrific music documentary, but who would think of it in those terms? That's like saying "Bowling For Columbine" is a great movie about guns.

Actually, it's unfair to invoke Michael Moore here, since the directors of "Dixie Chicks," Barbara Kopple and Cecilia Peck, don't wear their agenda on their sleeves. They straight-forwardly document what happened to the Chicks after lead singer Natalie Maines told her cheering London audience in March 2003 that she was "ashamed the president of the United States is from Texas."

Once the press picked up her comment, the group became country music pariahs and their bookings dwindled. Ms. Maines's remark particularly galled many of her hard-core fans because it was uttered outside the US. The biggest-selling female group of all time has been gamely fighting back ever since.

Kopple, who has directed two documentary masterpieces, "Harlan County, U.S.A." and "American Dream," and Peck, who produced Kopple's 2002 TV documentary "The Hamptons" and is Gregory Peck's daughter, astutely capture how the Chicks attempted both to make nice and stand fast.

From the get-go, Maines never backs down from her statement. The other Chicks, Martie Maguire and Emily Robison, clearly wished Maines had kept silent, but they support her throughout.

I suppose one could put a cynical spin on their steadfastness – why break up the band and lose all that moolah? – but that's not how it comes across. These women obviously care a lot about one another, and they have families and children who are just as much a part of their lives as their music.

They even seem to enjoy the controversy, posing near-nude for an Entertainment Weekly cover as if to tell the rabble-rousers, "You still like looking at us, don't you?"

The filmmakers had impressive access to the group, and the results are eye-opening. When Maines receives a highly credible death threat days before a concert, we see how the situation is handled – and its effect on her. In a hotel suite, Maines watches Tom Brokaw on television questioning President Bush about her statement in London, then launches into a diatribe that makes her London dig seem tame.

This movie brings out the irony that Maines's in-your-face spiritedness – so integral to the Chicks' appeal – pushes her to say things that end up turning off longtime fans. You can't have one Maines without also having the other. The film may be subtitled "Shut Up & Sing," but you can't sing with your mouth closed. Grade: A–

• Rated R for language.