One hundred jobs are to be cut at the Ministry of Education before next June, the public sector union says.

Ministry staff were told today about the job cuts, on top of about 300 vacancies not being filled, and were assured that the changes would not add to already heavy workloads, Public Service Association national secretary Brenda Pilott said.

"The ministry appears to have no strategy for how these cuts will be made; all it has said is that vacancies will not be filled.

"This means some teams will be hit harder than others and workloads will explode due to them being under-resourced," she said.

The redundancies would not improve services or bring greater efficiencies.

"The prime minister says he wants more schools to teach Mandarin yet, as a result of its approach to not fill vacancies, the ministry's national office team supporting the learning languages area of the curriculum has shrunk from three people to one."

Staff were also unsettled and uncertain as a result of the reviews.

"The ministry has been through a dozen reviews in the past three years, some of which are ongoing. One would have thought that after so many endless reviews, the ministry would be an effective and nimble beast," Ms Pilott said.

"Yet it has been criticised as one of the worst government departments in a recent trans-Tasman report."

The job cuts were part of an ongoing programme, Education Minister Anne Tolley said.

"It was signalled in March when I announced that the ministry would be reshaping its role, size and focus to give more frontline support to schools, with less national office bureaucracy," she said.

It was an operational matter for the ministry's chief executive, she said.

Education sector union the New Zealand Educational Institute, which represents 800 staff at the ministry working with special needs children, said the staff cuts must not target frontline jobs or compromise services to vulnerable students.

Cutting 100 positions would further risk the quality of New Zealand education, Labour MP Grant Robertson said.

The Government had made an election promise to cap public service jobs, not to cut them.

"While I understand that in the current economic climate it may be necessary for the Government to find efficiencies within our state sector, we need to ensure that kiwis continue to receive a high standard of public services," he said.

"It won't be long before the number of staff being cut from Ministry of Education will be reflected in student achievement."