RSPCA warned that it was dangerous to use a laser to scare off geese after King's College adopted this unusual method.
In last March, porters at King's College began using a hand-held laser gun to scare the goose away from the official lawn, but denied it was inhumane.
This deterrent was adopted after a group of continuing Canadian geese began to get dirty on the lawn, diving bombing queues waiting to hear evensong's visitors.
In response to concerns about goose welfare, RSPCA said that lasers should not be exposed to the eyes of animals, and that the technology has not yet been proven humane or effective by researchers.
However, the animal welfare charity did not criticize the college and would remain open if it proved safe.
A spokeswoman for RSPCA said: "Like humans, we do not support direct laser exposure to the eyes of animals.
"However, we realize that the indirect use of lasers to stop the gathering of problematic birds is No.
The lethal deterrent method that researchers are currently testing.
"If this approach proves to be effective and humane, it will certainly be welcomed by RSPCA.
Meanwhile, the college says the technology has proved effective this summer.
Philip Isaac of Domus bursar told reporters that its war on geese will also continue to "refuel goose eggs" to reduce the number of young chicks in spring.
He told the Daily Telegraph: "The geese in Canada are big bully birds and they scare off native birds, so there is no one here now.
"Two years ago we had about 50 geese on the back lawn and the problem got out of control because they were full of feces and attacked the public in the church waiting in line for evensong.
"We used some deterrence to get them out, and last year they seemed to find a better place to go, but they came back this summer and again caused trouble.
"The laser torch seems to be working at the moment, and we will also refuel the eggs in the spring to reduce the number next summer.
The comments came after students staged a highly public protest in last March against what they thought was the goose's "cull --
Things that the university strongly denies
A spokesman for King's College said: "The college uses a variety of non-
Harmful measures to stop the goose and will continue to do so.