Low pay, understaffing and a lack of professional support was sapping the morale of the workforce, she said.
Dr Powell said the base rate of psychologists working in public health was no match to those offered by the private sector as well as ACC and Corrections.
Northland DHB acting general manager mental health and addiction services, Neta Smith, said there were contingency plans to minimise disruption during the strike.
"This ensures people presenting with distress during the strike period will have their needs identified and access to other supports.
"A direct impact of the strike action is some may experience a longer wait to access specific interventions that psychologists would provide," she said.
APEX said despite the government's stated intentions of increasing access to psychological services for New Zealanders, it has not yet seen any new offer from DHBs to settle the national collective agreement for psychologists on terms attractive enough to recruit and retain these specialists.