Jobs will go at PrimePort, with announcements expected in the next two weeks.
Port workers yesterday joined the picket line at Timaru's Caroline Bay Trust Aoraki Centre opening, where they yelled their frustrations.
The port company is losing its container trade, which makes up a significant portion of the work.
PrimePort employs 55 staff and 30 casual workers.
The protest followed a meeting between port management and the union yesterday morning.
Rail and Maritime Transport Union organiser John Kerr said there was an overwhelming likelihood there would be substantial redundancies at the port.
Workers heckled Prime Minister John Key as he arrived to officially open the Caroline Bay Trust Aoraki Centre.
It was an irony that Mr Key was coming to open the pool, when the port was closing, Mr Kerr said.
"Management are going to come to us with a firm proposal in the next two weeks," he said.
"Part of the response is that we think this is a consequence of a government that leaves transport infrastructure decisions to the vagaries of the market.
"We want to send the Prime Minister a clear message that government should step in for the good of all New Zealanders.
"In a country of four million people, we need a national strategy so we can dictate terms to shipping companies, not them to us.
"In New Zealand, the ports are owned by regional councils, which means that shipping companies are not covered by the Commerce Act; if we had a national strategy we could cut all of that out."
Port chief executive Jeremy Boys confirmed that he had met staff yesterday. "It will be several weeks before a definitive proposal can be presented for consultation.
Mr Boys acknowledged that the impact would be substantial.
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