Hamilton-based bus company Go Bus says it's less than impressed with First Union calling a short strike notice for Monday morning.
The strike will affect Hamilton city bus services for two hours from 7:30am.
Go Bus says it only received the official strike notice on Sunday morning, but the union disputes that.
"At a meeting on the 23rd of March the company was advised by First Union that members would be balloting for strike action," says spokesman Jared Abbott.
"Further, First Union reported in a release last week that strikes would be occurring in Hamilton this week, and subsequently Hamilton staff were threatened by the company on Friday with disciplinary action if they wore their uniform while striking."
School bus services and Specialised School Transport Assistance services will not be affected.
Go Bus CEO Nigel Piper says the company has "a proud track record of increasing wages beyond the level of inflation" and a "good record of successful negotiation with the various other unions".
The Hamilton strike follows industrial action by Go Bus employees in Te Awamutu and Otorohanga last week. Mr Piper said at the time paying the living wage wasn't possible, as it would cost "in excess of $13.6 million" a year.
He on Sunday would be happy to increase pay to the living wage if the "council elected to stipulate a specific wage rate... provided it was applied to all operators with contracts and the cost to move to a higher rate was fully recoverable".
Go Bus says it will do "everything it can" to keep services running.