The Service and Food Workers Union (SFWU) says it will be taking legal action against the Southern District Health Board for jeopardising vulnerable workers.
The board has approved a plan to contract international catering company Compass to run its hospital kitchens; up to 20 percent of kitchen staff could lose their jobs as a result. The plan promises savings of at least $7 million over 15 years.
The board made the decision on Thursday after two years of debate.
The union's Southland organiser Anna Huffstutler said the DHB was not acting in good faith, and that was exemplified by the union being shut out of the decision-making process.
"It was quite an insult, absolute insult, that HBL (Health Benefits Limited) and Compass were allowed in the closed part of the board meeting yet when a couple of members of the board asked if we could attend, we were completely shut down," she said.
"So what does that say - does it say that the government's put so much pressure on the DHB to accept that? I don't know."
Ms Huffstutler said the union hoped the decision would be reversed and it could enter into mediation talks with the DHB.