The Tonga Privy Council says the Government's plan to ratify the Convention on the Elimination of Discrimination Against Women is unconstitutional.
King Tupou VI, with his Privy Council, was responding to petitions from groups in Tonga who have sought his help to stop the ratification process.
The Government has committed to ratify the document but has put this on hold until after this week's coronation of Tupou VI.
The King, in a statement, says he wants to acknowledge the concerns of 13,048 of his subjects who have sent eight petitions to him.
The statement says the Privy Council is not persuaded that the process followed by the Government is in accord with the constitution.
It says the Council has not authorised ministers to sign the document.