The union representing teachers in Tasmania has been accused of bullying staff, acting in an anti-union fashion and creating a culture of mistrust.

The ABC has obtained a letter that was sent to about 50 Australian Education Union (AEU) councillors on behalf of staff who are represented by the Australian Services Union (ASU).

The AEU in Tasmania represents about 6,000 education workers, and is headed by Roz Madsen, who is also the president of Unions Tasmania.

The damning letter outlines questionable redundancies and the disregard of an existing staff agreement as the union undergoes a restructure.

The ABC understands almost a quarter of the 21 AEU staff are on stress-related leave or have made workers compensation claims.

"We are informed that over a long period some employees perceive or believe that they have been subjected to bullying," the letter reads.

"We believe that the recent changes that are being made under the restructure are not in line with union values and beliefs."

The letter claims that under the restructure, some workers had been made redundant only to be replaced by contract workers.

It said the ASU is of the view that the AEU is "unreasonably disregarding" clauses in an existing staff agreement, while a new agreement is negotiated.

Negotiations have been going for 12 months, unsuccessfully.

"We are not against the changes being made to the AEU … however the resulting outcomes for some of your AEU staff has been disappointing, with many people being unfairly disadvantaged and treated without due regard to reasonable union values and industrial relations procedures," the letter reads.

'Mental health, wellbeing of teachers affected'

The ASU, which represents most of the staff, claims employees who hold permanent positions have been told they will need to apply for new fixed-term contract roles or that they no longer have a job and will be made redundant.

"Is this ethical or moral for a union organisation to behave in this way towards their employees?" the letter asks.

"The mental health and wellbeing of some staff has been affected, which has resulted in two employees claiming workers compensation and others having to take sick leave due to the stressful situation that they have found themselves in."

In a statement, AEU Tasmania state manager Roz Madsen said the union had "undergone some changes in order to better serve the interests of Tasmania's hard working teachers, principals and support staff in our public schools and TAFE".