Theater chains are taking sides in the “Bully”-rating showdown: Second-largest exhib AMC will allow minors into theaters with parental permission, while No. 3 chain Cinemark says it won’t show the unrated pic unless the Weinstein Co. submits an R-rated version.

The nation’s largest chain, Regal, said Wednesday that it will screen the docu, but will adhere to the MPAA’s traditional R rating guidelines requiring that minors be accompanied by a parent or adult guardian.

AMC is essentially treating “Bully” as an R-rated film, but with one key difference: Under-17 moviegoers need a written note, though it will also accept verbal permission (mom on the other end of a teen’s cell phone, for example). Exhib also will provide permission slips on its web site and at the box office.

Theaters usually treat unrated films like NC-17-rated pics, which prohibit any person under 17 to attend — or in the case of Cinemark, opt not to screen the film at all.

Lee Hirsch’s “Bully,” an expose on bullying in U.S. schools, has been at the center of a highly-publicized ratings battle, after the MPAA assigned an R rating because of language. Ultimately, Weinstein announced Monday it would release “Bully” unrated by the MPAA after failing to obtain a less-restrictive PG-13 rating.

AMC’s overture marks a small — though not insignificant — victory for the film, especially as Weinstein broadens “Bully” to additional AMC locations over the coming weeks.

“Bully” bows limited Friday at five locations, of which two are AMC: New York’s Lincoln Square and Century City in L.A.