The challenge to the opening of Tonga's parliament is expected to be heard by the Supreme Court in an urgent session once a statement of defense is put forward.
A civil action has been brought by Tonga's Noble Lasike and eight People's Representatives, over Princess Pilolevu opening parliament when the constitution calls for the king to do so.
According to one of the representatives, if the king is unable to be present, a committee of three nobles can be called on to perform that function.
The civil action alleges that whatever the current session of parliament passes in terms of legislation, could be rendered null and void as a result of this issue.
The prime minister, Dr Feleti Sevele, has said the process was legal.