UPDATED 7.04PM: It's become a battle of the finest contractual detail.

LISTEN ABOVE: Larry Williams spoke to Dr Deborah Powell about the strike going ahead tomorrow. 

Just over 3,200 out of New Zealand's 3,500 resident doctors will take strike action for 48 hours starting at seven tomorrow morning.

The New Zealand Residential Doctors Association said its a dispute over consecutive days worked.

Lead Chief Executive for Employment Relations of New Zealand's 20 DHBs Julie Patterson said it has already agreed to fewer days worked in a row, and has offered a pay rise of five percent over three years.

"So at the moment on average junior doctors work 53 hours a week and they earn somewhere between $90,000 and $120,000 thousand dollars, so it's a five percent increase on that."

But the New Zealand Residential Doctors Association said it didn't request more money.

The association said the comment is a red-herring from DHBs to distract form a health and safety matter where staff are not getting the adequate time to rest up for their next shift.

Association national secretary Dr Deborah Powell said the increase that's been offered was part of a Consumer Price Index adjustment to match inflation that health workers receive in due course anyway.

She said they're not after a pay rise, and a commitment to fewer hours from DHBs isn't enough - they want it to be a contractual obligation.

"We've been working on this for four years now and had only limited success so at this point and time we want a contractual obligation that these hours will drop."

However Julie Patterson said if they contractually commit to no more than ten consecutive days work, junior doctors will end up being paid for two days they don't actually work because of a clause in their contract, and how hours are calculated in that clause.

"All 20 DHBs are concerned about the health and safety claims the union has made, we do not want fatigued workers, of course we don't, but we have to have some movement from the union in relation to the contract clause."

The association simply said that's not true.

"Resident doctors are on a salary, that salary is tied to the number of hours they work in a week on average, and it's done in five hourly blocks so they get a salary if they work between 55 and 60 hours, or between 60 and 65 hours a week.

"If their hours of work drop out side one of those five hour blocks then their salary drops along with it."

Meanwhile a DHB spokesman said specialist doctors working without the help of junior doctors over the 48 hours will be receiving between $280 and $500 dollars more per hour than they normally get paid.