About 3000 school support staff will go without pay for a fortnight in February, following a dispute over an extra pay day next year.
There are 27 pay days in 2017, rather than the usual 26, the Ministry of Education says.
The ministry was going to pay the staff on each of the 27 pay days, at a reduced rate per pay, but the Employment Court ruled that was contrary to their collective agreement.
The ministry said instead the support staff would be paid on 26 pay days at their regular rate, with no pay on the 27th pay day.
It said they would get the same amount per year, whichever way they were paid.
The NZEI said it was disappointed and would be talking to its lawyers.