The union says the strike action will cover two of the three laboratories currently testing for COVID-19. These are two DHB labs - LabPLUS in Auckland and Canterbury Health Laboratories in Christchurch. The third is ESR, which is not covered by APEX.

The strike will accompany ongoing partial strike action that will run until May.

The processing of COVID-19 samples will continue - but in the face of "considerable disruption" to the labs where the testing takes place.

"The employers have made no effort to reach a fair agreement," senior APEX advocate David Munro says. "The employers' most recent offer discriminates against our members and would lock them into inferior salaries for the term of the collective agreement and beyond."

Despite APEX's laboratory scientist members holding university qualifications, they earn 12 percent less than a similarly qualified, registered nurse. They also earn more than 7 percent less than identically-qualified colleagues working alongside them, but on a different employment agreement, according to the press release.

Munro claims that employers are unprepared to settle the dispute and eliminate the disruption to the labs.

"It couldn't be a worse time. Now is when we should all be pulling together to fight coronavirus. Instead the employers prefer to fight their own staff."

Director-General of Health Dr Ashley Bloomfield said during a press conference on Monday that the timing "wasn't very good", but reiterated the strike will not impact testing for COVID-19.

"That strike will not affect our laboratory testing for COVID-19. Either the workers are not in laboratories, like ESR, there are no members in that lab. Or where they do have members in the Auckland lab, they are not involved in COVID-19 testing."

Dr Bloomfield said he's "disappointed" that the union are using the situation as "leverage".

"I'm disappointed they are using this situation to get leverage around an industrial matter that has been ongoing since last July... I don't think now is the time."