Poland's former presidents and other leaders have expressed "anxiety and opposition" at what they say is the loss of authority of the Constitutional Tribunal in the current crisis surrounding the court.

The ruling Law and Justice party, which won a parliamentary majority in an October election and also has an ally in the nation's president, is aiming to gain influence in the tribunal in a way that the opposition and critics say is unconstitutional and undemocratic.

Fifteen politicians published their statement in pro-EU Gazeta Wyborcza daily on Tuesday.

They said observing the rule of law is especially important when "all the power is in hand of one political option."

Among those signing are former presidents Bronislaw Komorowski and Aleksander Kwasniewski and former foreign ministers Radek Sikorski and Grzegorz Schetyna.