Subscribe | UPI Odd Newsletter Subscribe NEW YORK, Feb. 10 (UPI) -- Authorities in New York said a marketing company did not have permission to promote "The Walking Dead" by hiding "zombies" in a subway grate. A spokesman for the Metropolitan Transportation Authority said Sunday the organization and police are investigating after a video was posted online Wednesday featuring actors portraying zombies and scaring people by clawing at them through a subway grate in the city, the New York Post reported Monday. Advertisement The clip also shows the "zombies" preparing for the stunt by prying the grate open and climbing inside. "We are deeply troubled by this video," the spokesman said. He said marketing company Relevant did not have permission from city officials to stage the stunt, which was designed to promote AMC's zombie-themed series "The Walking Dead," which returned with new episodes this week. Police said the incident is being investigated and could result in charges including trespassing, disorderly conduct and criminal mischief. Relevant officials did not return calls for comment, the Post said. Read More Norwegian high school class learns from 'The Walking Dead' game 'Walking Dead' mid-season finale watched by 12.1 million 'Walking Dead' renewed for fifth season AMC developing 'Walking Dead' companion series Man says he stole truck because he was being chased by zombies