The Hamilton City Council and the Public Service Association have clashed after half the union members who responded to an internal survey claimed they had been bullied at work.
The PSA said the result highlighted a culture of bullying, a claim council leaders dispute.
The survey was conducted in June and 54 of the PSA's 129 members completed it - which represents 5 per cent of all staff.
Of those who filled in the eight-question survey, 50.94 per cent said they had been subjected to bullying in the previous six months, and a quarter said they experienced negative behaviour weekly or more frequently.
In the report, the PSA said the results suggested "a serious bullying problem" which was consistent with feedback from members, the council's own climate survey and media reports.
The negative behaviour staff alleged included withholding of information affecting performance, being ignored or excluded, persistent criticism of errors and mistakes, allegations against them and exposure to excessive teasing and sarcasm.
More than a third of those surveyed (38.9 per cent) felt they had little control over their workload, 33.3 per cent felt they did, and 27.8 per cent felt indifferent.
PSA national secretary Brenda Pilott said the council should be concerned.
"The PSA believes bullying is a serious issue facing Hamilton City Council, and the organisation would gain credit from the wider community if it were seen to be acting proactively."
Council chief executive Barry Harris told the Herald that, through his observations, he did not believe there was a bullying culture.
"I believe there are instances of bullying behaviour, as there will be in all organisations," he said.
"I certainly take them very seriously and I know in the past and now every case is properly investigated."
The council has defended refusing to let the PSA survey all staff because the union has no jurisdiction overnon-members, but the two partieshave agreed to meet to discuss the results.