The Engineering Printing & Manufacturing Union is angry a $20 million Government contract is going offshore.
The NIWA research vessel, Tangaroa, is getting new equipment installed, including a dynamic positioning system, which allows it to stay in one spot, despite pressure from tides, currents or wind.
A company in Singapore won the contract over a New Zealand consortium headed by VT Fitzroy, a marine firm in Devonport.
EPMU national secretary Andrew Little, says the work could have been done in this country.
However, Research Science and Technology Minister Wayne Mapp, says the offshore tender was several million dollars cheaper.
VT Fitzroy says winning the contract would have provided 12 week's work for 40 to 50 people.
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