The Advertising Standards Authority has received a number of complaints about the Tulleys Farm Shocktober Fest bus advert which features the image of a female zombie covered in blood.
Critics claim it is too scary and the feature is currently being investigated to see if any rules have been broken.
The adverts are on the sides of over 100 buses - some of which pass through Horsham - operating across Sussex and South London including Crawley, Croydon, Kingston upon Thames and Tunbridge Wells.
Stuart Beare organiser of the Tulleys Farm Shocktober Fest event, said: “We do not intend to cause offence to anyone. The image of the zombie girl on our advertising is no worse than many images you’ll see at this time of year in newspapers and magazines, on the Halloween costumes in the supermarket isles and even kids TV programmes.
“We have been running our Halloween events for over 15 years, and they are extremely popular with up to 5,000 people a night going through the six haunted houses and rides.”
The farm is waiting for the Advertising Standards Authority to come back with their judgement to see if it has to take the ads off the buses.
Tulleys Farm Shocktober Fest Scream Park is open selected nights until November 2 www.tulleyshalloween.co.uk