School governors have refused to divulge the cost of their defence in the High Court against a successful race and religious discrimination claim brought by a Sikh pupil.
Ann Clwyd, Labour MP for Cynon Valley, has written to Aberdare Girls' School asking it to reveal the final bill and whether it was taken from the school budget.
But the school has blocked the request, saying it does not have to give details under the Freedom of Information Act. Ms Clwyd said she would now appeal to the Information Commissioner, and that the public had a right to know how much the case cost.
Last month Sarika Watkins-Singh, 14, won her legal battle to be able to wear her "kara" bangle, one of the 5Ks in her faith, in class.
She was excluded from school last November for refusing to remove the bangle. But the school had to mount its own defence after the local authority withdrew funding.
Mr Justice Silber ruled that Ms Watkins-Singh was a victim of unlawful discrimination on the grounds of race and religion and rejected the argument that she was in breach of the uniform code.
Ms Clwyd, who backed Miss Watkins-Singh's case from the outset, said: "I wrote asking how the legal costs were going to be paid, what their liabilities were, and how much it would cost in future. I am concerned over the cost."
The MP said Rhondda Cynon Taff also rejected requests for the information. A spokeswoman said the spending of the school budget was a matter for the head and governors, and not the local authority.
Ian Blake, chair of governors, said the school had sufficient funds set aside and pupils would not suffer financially because of the case.
"We would not have entered into this without checking that we could afford to pay for it," he said.
But he refused to give details and said the governing body did not yet know the full cost of the case.
Ms Watkins-Singh will return to the school in September.
The governing body has said it will not appeal against the ruling. It has now asked for a meeting with the local authority to discuss the uniform policy and guidance that bans all jewellery except for wristwatches and stud earrings.
Peter Wilby, page 20.