Lawmakers from Poland's ruling party have added to a political crisis surrounding the constitutional court by voting in a new member to join the already overpopulated tribunal.

But the parliament vote on Thursday was itself confused and contested, with the main opposition party demanding a repeat vote.

Opposition leaders complained that one lawmaker violated regulations by voting for the new judge for the Constitutional Tribunal both in her own right and on behalf of an absent colleague, with his consent.

Poland is under criticism from the European Union, which says the conservative government's policies relating to the tribunal threaten democracy and the rule of law. The government's efforts to put loyal judges on the panel have led to too many appointments and to the court's paralysis.