Public hospitals' chronic industrial troubles have worsened after what unionists consider a "very provocative move" against radiographers by district health boards.

Radiographers employed by 19 DHBs have been engaged in low-level industrial action for months, which flared into full strikes for a time after snail's-pace pay talks.

The DHBs announced their surprise move yesterday, saying: "After 14 months of negotiations, nearly 600 strike notices and five offers on the table, district health boards are calling it quits with Apex, the union representing medical radiation technologists."

They withdrew their offer of two 1 per cent pay rises.

Once collective agreements have been expired for a year, they become individual deals with each former member of the collective, a major disadvantage for a union.

Apex - the Association of Professionals and Executive Employees - said the boards' action would increase hostilities.

"It is a very provocative move and will almost inevitably lead to an increase in industrial action," said union spokeswoman Robyn Slater.

She said it was hard to understand the move, "when negotiations were so close to settlement".

Worsening relations between the parties comes amid renewed strike action by one associated union, the Medical Laboratory Workers Union, and an improvement in the outlook for pay talks with another, the Resident Doctors' Association.

Auckland DHB' unionised lab workers were on strike on Monday and yesterday, and Counties Manukau workers are out from midnight on Monday until midnight tonight.

Counties Manukau asks people who need help for a condition that is not life- or limb-threatening to contact a GP or accident and medical centre rather than going to Middlemore Hospital's emergency department.

"In a life-threatening situation always call 111," the DHB says.

The Resident Doctors' Association was edging close to strike action last month after choking on a radical proposal by the DHBs to rewrite their national collective agreement.

But after balloting members on improved terms, the association is seeking further talks with the boards.