The Department for Education and Employment has been censured by the Data Protection Registrar over its attempt to collect teachers' home addresses.
The ruling, which follows a complaint from the National Union of Teachers, means the Government cannot mail free copies of its Teacher magazine direct to people's homes as it had intended.
Schools had been asked to send the DFEE the addresses for pension purposes and for the General Teaching Council elections.
But now the Data Protection Registrar has asked the department to confirm that it "will not make use of teachers' personal data to send them personal copies of Teacher magazine containing commercial advertising", a move which delighted the union.
General secretary Doug McAvoy said: "The NUT's stand has been vindicated. We advised members not to complete the Government's forms. We challenged the Government."
The department must also "explain why it, as opposed to the council, requires the home addresses of potential members of the GTC".
Following a recent decision by the Data Protection Tribunal on a similar case, the department will be required to get positive consent from teachers to use data in order to send them a magazine containing commercial advertising.
The NUT has provided its members with forms for the department saying they do not want their names to be used for the purposes of direct marketing.
A spokeswoman said the DFEE would be responding to the registrar's concerns.