Students held a "big kiss" protest at a Sainsbury's in Brighton after two women were asked to leave the store for kissing.
The couple, one of whom is a student at the University of Sussex, had been shopping at the New England Street supermarket in the city on Saturday.
A customer complained after one of the women gave her partner a peck on the cheek.
Sainsbury's later apologised and offered to donate £100 to a charity.
The protest was organised by the university's students' union, which has urged the supermarket giant to review its policy on equality and diversity.
About 200 people gathered outside the store before some of them turned to kiss each other, saying they wanted to "turn the negative into the positive" and highlight equality in the city.
The women were asked to leave the store by a security guard, who was not directly employed by Sainsbury's.
In a statement, a spokeswoman for the supermarket chain said the couple "were not behaving inappropriately and we are very sorry that they were treated in this way".
She added: "Had a senior manager been made aware of the original customer complaint, they would have followed our guidelines and no action would have been taken."
The Students' Union said the supermarket's response was inadequate.
It said the "Big Kiss In" was open to everyone, regardless of sexuality, "to highlight that whomever you wish to kiss, it is to be celebrated".
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