NEW YORK (PIX11) — The MTA has filed a formal complaint with the NYPD over a zombie prank promoting the hit AMC show, “The Walking Dead,” a spokesperson for the authority told PIX11.

The stunt, which featured actors dressed as zombies and hiding underneath sidewalk grates in Union Square, was a promotion for the show’s new season.

City officials say permission was never granted. Permits are required for shoots that use public space.

The production company, that is responsible for several other similar stunts, has not commented.