Late on Wednesday, Brad Widders became the fourth councillor to resign from Armidale Regional Council.
His resignation followed those by mayor Simon Murray and deputy mayor Libby Martin this week, while Diane Gray was the first to go, resigning in early June.
In a post on social media, Mr Widders said he handed his resignation to administrator Viv May because it would be untenable to achieve anything with the remaining councillors, following the first three resignations.
"My decision was largely based on the continued displays of unacceptable behaviour by the remaining councillors," he said.
"This has been demonstrated very clearly towards to myself, other councillors and council staff. This behaviour has been appalling, the community deserve better."
He thanked the community who supported him, and indicated he would run for council again at the next election.
"It's not the end it's just a pause and I hope that I can again gain your support at the next election as I will be running again."
The resignations this week followed the announcement that CEO Susan Law will go at the end of this month.