Canal Walk shopping centre has two fights on its hands - one against criminals and another against legal firearm owners who like to shop armed.
After four robberies, the mall banned guns, leading to the creation of a Facebook page called Firearm Owners Boycott Canal Walk.
The group is urging supporters to visit Canal Walk's Facebook page and give the mall a one-star rating.
Said one user: "We can halve their current rating of 4.3 stars to about 2.5."
Gun Owners South Africa spokesman John Phillips said the campaign had lowered Canal Walk's rating to 4.0 in two days.
Mall CEO Gavin Wood said: "It is our understanding that as private property, we are permitted to implement reasonable restrictions upon entry provided these are appropriately communicated to our customers."
Gun Free South Africa spokesman Claire Taylor welcomed the ban.
"If there is a robbery and somebody pulls out a gun, there is a risk that somebody else could get shot and killed," she said.
Additional reporting Aphiwe Deklerk
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