A fast-track teaching scheme has been breaking the law by putting people into a job without the position being advertised, the Employment Relations Authority says.
However the Education Ministry is standing by the scheme, saying the schools where it has been introduced report it is making a difference.
The Teach First scheme puts university graduates through an intensive eight-week residential training programme before placing them in a paid teacher-training position in a low decile secondary school for two years.
But the Employment Relations Authority said they were teaching jobs and should be advertised, and the best person selected.
The law will have to change to let the programme go ahead.
Education Ministry spokesperson Lisa Rodgers said the scheme has had strong support from many principals and schools who reported it was making a difference to them.
She said the ministry was considering the ruling before deciding its next step.
Teach First said it too was considering the implications of the ruling.
Post-Primary Teachers Association president Angela Roberts, who complained to the authority, said she hoped Teach First would abide by the ruling.
"They've had these options to talk about and consider and actually get done for a very long time, and what they did was take a risk, take a punt, knowing that we were going to the authority and not really considering what they may have to do if they were proven wrong."