One employee of the National Association of Head Teachers claimed that staff felt they were operating in an environment akin to the Stasi.

Amicus, the union representing the NAHT headquarters staff and regional officials, balloted members because it said the association had refused an independent inquiry into their allegations.

It claims that the NAHT management has been secretly monitoring staff emails and has demanded the lifting of disciplinary action against one of the association’s London regional officers, suspended in February for possible gross misconduct over the content of an email.

Of the 28 staff balloted, 23 voted for action and one-day strikes have been scheduled for July 4, 12 and 20. As The TES went to press talks were continuing between the two sides to try to avoid the action. They were expected to take the dispute to the Advisory, Conciliation and Arbitration Service.

Barry Jones, Amicus regional officer, said: “The ballot result is exceptional and an indication of the strength of feeling among NAHT staff.”

David Hart, general secretary of the NAHT, has written to Amicus admitting that Kathy James, an NAHT senior assistant secretary, technically could access other employees’ emails but stressed that she did not know this.

He said that an independent inquiry by the IT company used by the association had found no evidence of email monitoring by senior managers.

But Amicus dismissed the IT firm’s investigation as a “purely technical” exercise. It said the suspended regional officer had been prominent in lobbying against an office restructuring over which staff felt they had not been properly consulted.

It has lodged a formal complaint with the information commissioner about the allegations of email monitoring.

Mr Hart confirmed the union was in negotiations with Amicus. Responding to the Stasi claim, Mr Hart said: “That is a completely outrageous allegation that has no foundation whatsoever.”