A Northland student is struggling to become a qualified teacher after being forced out of a school placement by a teachers' union because he works at a charter school.

This is despite the Ministry of Education saying the Post Primary Teachers Association (PPTA) had no authority to make that decision. The student, who did not want to speak publicly, now faces an uncertain future with the possibility of not finishing his studies.

The man started at Te Kura Hourua O Whangarei Terenga Paraoa in Whangarei this year as a teacher. He had a bachelor's degree and was employed on the proviso he would study towards a post-graduate diploma in teaching through Massey University. But just three days in to his first placement, at Tikipunga High School, he was asked to leave.

Te Kura Hourua O Whangarei Terenga Paraoa principal Nathan Matthews said while he knew about the ban, once the student was accepted by the school he thought it would be okay.

"It hit him quite hard," Mr Matthews said. "He felt like he was being discriminated against."

The nation-wide ban involved PPTA members, the majority of teachers, limiting and avoiding where possible professional interactions with charter school employees. Tikipunga High School board of trustees chairwoman Veronica Turketo said the school was unaware the student worked at the charter school when it gave him the placement.

"When our members became aware of the student teacher's employment at the charter school the PPTA position was followed," she said.

Ministry of Education head of student achievement Graham Stoop said ultimately the board was responsible for the decision.

"It is not appropriate that a school refuses to accept a placement because staff at the school, or the union representing some of the staff, are running an industrial campaign against the student's place of employment," Mr Stoop said.

"The PPTA has no responsibility or authority to influence these decisions and it is disappointing if they have used their influence to stop a student-teacher receiving all of their training because they disagree with the student's employment choices."

The ministry had contacted the school and PPTA about the issue.

Northland central regional PPTA chairwoman Adele Towgood said the majority of teaching staff would not work with charter school employees.

"The charter school ban was discussed and agreed upon by members nationally as being the grass roots response to the introduction of this unnecessary legislation," Ms Towgood said.

PPTA national president Angela Roberts said the student could do his three required placements at charter schools or private schools.

Both teaching unions and opposition political parties are opposed to charter schools. Professor John O'Neill, director of the Massey University Institute of Education, said he was optimistic the student would complete his training.