DUP councillors walked out of a council meeting over a discussion about flying the rainbow flag to support LGBT people.
The row happened on Tuesday night as Causeway Coast and Glens Borough Council considered flying the rainbow flag for Belfast Pride.
Alliance councillor Chris McCaw, one of the few openly gay politicians in Northern Ireland, said he was "very sad, and actually quite hurt" by the walkout.
"Flying a rainbow flag for one day from council headquarters would be a small yet very significant gesture towards a marginalised community in the borough," he said.
Sinn Féin councillor Cara McShane said her party "proposed that the rainbow flag should fly for one day to mark Pride".
"It's disappointing that DUP councillors refused to discuss the proposal and then walked out of the meeting," she said.
"This is further evidence of the DUP's failure to embrace equality for all citizens."
The DUP's council group said it "had to regrettably withdraw" because Sinn Féin "decided to ride roughshod over procedure by introducing a last-minute agenda item which not all members were aware of".
"This was not acceptable to us as a group and would fly in the face of Standing Orders. Our only course to stop this happening was to walk out and bring the meeting to a halt," the party said in a statement.
Armagh, Banbridge and Craigavon Borough Council earlier this week agreed to fly a rainbow flag to coincide with Belfast Pride.
