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.