He said there was systemic underfunding of the health system.
"Budget documents say DHBs expect a 17 per cent increase in demand over the 10 years to 2021, but they won't get the funding to match and they're planning to squeeze it out of staff."
The union will work with DHBs to make sure some staff will continue working to ensure patient safety. Those striking around the country include mental and public health nurses; physiotherapists; anaesthetic technicians; dental therapists, administrative staff and other occupational groups.
Graham Dyer, chief executive of Hutt and Wairarapa DHBs and chairman of the District Health Boards' Employment Relations Strategy Group said the union was not recognising the tight fiscal environment that DHBs are in.
He said bargaining for the six collective agreements has been ongoing for between one and 12 months.
"The co-ordinated timing of the action is clearly part of some other agenda.
"DHBs have offered the nurses and allied staff the same increases that have been accepted by other clinical groups in recent bargaining.
"DHBs do not believe there are any reasons to offer these PSA groups more than the increases that were accepted by similar work forces."
He said the public can be assured any effect on patients and services will be managed.
"We encourage the PSA to get back to the bargaining table as that's the only place the pay issue will be resolved."