Most of St John Ambulance's paid staff in Northland who are members of the First Union have decided against ditching their uniforms as part of ongoing industrial action.
Between 70 and 80, or nearly 90, per cent of St John Northland workforce are members of First Union but only about four have decided to wear T-shirts reading "Healthy Ambos Save Lives".
St John will next week deduct 10 per cent from the wages of its employees who are members of First Union and wear the T-shirts for not adhering to its uniform policy.
The wage deductions come as ambulance officers enter their third month of industrial action, following stalled collective agreement negotiations with St John.
On Friday Northland St John operations manager Tony Devanney said a small number of paid staff could be wearing black, union-issued T-shirts but the majority have decided not to, which was "great".
The First Union, which represents 1000 ambulance officers across the country, has condemned the move as "astounding".
But St John says it didn't take the step lightly, and it was done out of concern for the health and safety of staff and patients.
St John clinical operations director Norma Lane said ambulance officers needed to be easily recognisable to the public and other emergency service personnel.
It had amended its uniform policy to enable employees to wear the First Union T-shirts, but had also requested staff wear hi-viz vests over the shirts, and proper uniforms on their lower half.
Ms Lane said St John reached agreement with four of the five unions who represent its ambulance offices last year.
However, First Union rejected the offer and was taking industrial action to try to force a 2 per cent pay rise and additional leave, which St John could not afford.