Orderlies at Waikato Hospital in Hamilton were scheduled to start a second strike over pay and conditions from midnight Tuesday.
The 75 orderlies, out of just over 100, planned to walk off the job for 48 hours then.
The orderlies, who are members of the Unite Union, first took industrial action at the end of January for 24 hours.
The union says the Waikato District Health Board declined to attend mediated bargaining offered by the Department of Labour.
A union organiser, Jared Philips, says the board is acting irresponsibly.
The board says it will not negotiate with its orderlies while they are on strike.
Its employee relations manager, Greg Peploe, says claims from the union that the board was in breach of the signed bargaining process agreement were incorrect.
He says the board will only sit down and talk once strike notices are withdrawn.
Mr Peploe says the orderlies' industrial action will have minimal impact on patients and the public.