The MPAA said the decision was based on the film's "violent and disturbing images and for language."
The Reporter said Lions Gate asked MPAA head Jack Valenti for an emergency appeal because the film is scheduled to open in less than two weeks.
Lions Gate Films Releasing President Tom Ortenberg said the MPAA rating was completely unjustified.
"We are adamant about overturning this decision in an expeditious manner to ensure that as many people as possible, including young adults who represent the future of our nation, are able to see one of the most important and thought-provoking films of our time in theaters on June 25," said Ortenberg.
"It is sadly very possible that many 15- and 16-years-olds will be asked and recruited to serve in Iraq in the next couple of years," said Moore. "If they are old enough to be recruited and capable of being in combat and risking their lives, they certainly deserve the right to see what is going on in Iraq."