Banksy's latest artwork was attacked as a "drunk halfwit" tried to damage the mural on a garage wall in south Wales.
A security guard chased the culprit away on Saturday as he tried to pull down the newly-fitted plastic screen that protects the Port Talbot graffiti.
Police were called and the local community fears the artwork may become a target for "some idiot who wants to make a name for themselves."
Extra security guards have been drafted in to protect 'Season's Greetings'.
"Some drunk halfwit has tried to pull the fencing down and the protection glazing at the Banksy artwork," Gary Owen posted on the local Facebook page he runs.
"This art is for Port Talbot, Neath and surrounding areas. We do not want it wrecked."
The mural was not damaged and police ultimately did not attend the incident at about 22:30 GMT on Saturday - just hours after half of the artwork in Taibach was covered by a protective plastic screen.
Hollywood actor Michael Sheen contributed towards the cost of the screen and the local movie star is also helping pay for the security.
"It's amazing and such an honour that Banksy chose to come and paint his latest piece in Port Talbot." added Mr Owen, the man who messaged Banksy in August to ask if he would paint a piece in Port Talbot.
"We should be treasuring this privilege and it's very sad that some people want to spoil it for everyone and give Port Talbot a bad name.
"I do fear it'll become a target for some idiot who wants to make a name for themselves - and that's sad."
The image appears on two sides of a garage in Taibach and depicts a child enjoying snow falling - the other side reveals it is a fire emitting ash.
A local businessman covered one side of the work with a temporary protective plastic sheet on Saturday afternoon - and on Sunday the other side will be covered.
A more permanent solution is expected to be installed in the new year.
Volunteers working to protect the elusive artist's latest mural said at least 2,000 visitors have turned up to see it over the first two days.
It appeared on Ian Lewis' breeze block garage on a lane behind Caradog Street in Taibach on Tuesday.
Traffic wardens have been drafted in by the local council to control traffic.
Banksy confirmed the image was his when he posted a video on his Instagram account on Wednesday.