ABC News 17 reports Goodrich Capital 8 Theaters in Jefferson City, Missouri wanted to get moviegoers excited for the film by dressing people up to resemble S.H.I.E.L.D. members, part of the Marvel world's secret intelligence agency.
(You can see the photo of the people here.)
Instead, several people dialed 911, prompting local police to respond.
The stunt comes less than a year after the "Dark Knight Rises" shootings at a theater in Aurora, Colorado during a midnight screening.
Captain Doug Shoemaker told ABC 17 News they received calls about a man dressed in body armor with a rifle walking into the theater.
"Everything was in place, it's the opening night of a superhero movie, it's somebody walking in all-dark clothes, everything pointed to bad things about to happen," said Shoemaker. "There's really no good that can come of this."
A retired Army war veteran told the affiliate the event triggered his post-traumatic stress disorder.
Another person at the showing commented on the theater's Facebook page that he "and 99.5% of the other people there realized they were S.H.I.E.L.D. operatives carrying fake guns."
Theater manager Bob Wilkins defended the stunt to ABC 17 News saying it was planned for months in advance and that many were entertained.
Wilkins did say the theater took the Aurora, Colorado
The theater has since posted the following apology to its Facebook page:
"We apologize and are sympathetic to those who felt they were in harm’s way with our character promotion for Iron Man 3. This was not a publicity stunt. We have worked with the Cosplacon group on many