The Government will pursue the Guardian newspaper for legal costs if it successfully blocks the publication of the Prince of Wales's letters to ministers.
Solicitor General Oliver Heald said if the Government successfully blocks the release of Charles's letters in the Supreme Court it will expect the newspaper to pay its legal fees "to protect public funds".
Guardian journalist Rob Evans has been trying to make the letters public under the Freedom of Information Act and in September 2012 a High Court ruled in his favour.
Government departments did not intervene but Attorney General Dominic Grieve overruled the decision a month later.
But earlier this month the Court of Appeal ruled that Mr Grieve had "no good reason" for overriding the High Court's decision and said his veto was incompatible with EU law.
Grieve claimed that releasing the letters would undermine the principle of the heir to the throne being politically neutral and was granted permission to appeal against the latest ruling to the Supreme Court.
Today at Attorney General questions Heald said if the Government is successful in the Supreme Court, it will seek to have all legal costs paid for by the Guardian.
He was asked by Labour's Paul Flynn (Newport West) in the Commons: "How much is the department spending to contest Freedom of Information decisions, court decisions, in order to suppress information to the public?
"The claim has been made that information is available that would show that an important person is unfit to do his future job.
"Shouldn't we allow the letters, the lobbying letters of Prince Charles to be made public?"
Heald replied: "You are raising a case which involves issues of constitutional significance, which includes upholding Parliament's intentions for the Freedom of Information regime and the Government's ability to protect information in the public interest.
"It is important the Government continues to fight the case in question.
"To protect public funds however if we are successful in the next stage of the legal proceedings we will expect the Guardian to meet our legal costs in full."