Bishop Stanislaw Wielgus' past was first revealed in newspapers

The decision was made at an emergency meeting of the country's 45 bishops triggered by the dramatic resignation of Warsaw's archbishop on Sunday.

Bishop Stanislaw Wielgus quit after he confessed to collaborating with the communist police.

A commission is to probe the past of all bishops and "people of the Church".

"The bishops have confirmed the will to carry out a full verification of the truth about ourselves" and all clergy, said Archbishop Jozef Michalik, the head of the bishop's council.

Correspondents say the revelations of collaboration have severely weakened the Church, to which 90% of Poland's 40 million people belong.

Bishop Wielgus announced his decision to resign at a service intended to install him as the city's new archbishop.

The canon of Krakow cathedral, Father Janusz Bielanski, stood down the next day for the same reason.

Bishop Wielgus confessed his past involvement with the secret police after Polish press reports appeared last month suggesting that he had been a longstanding collaborator.

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The BBC's Adam Easton in Warsaw says that in a country where the Catholic Church plays such an important role, this scandal could hardly have been more shocking.

The Church was highly esteemed because of its leading role in the fight against communism in Poland and worldwide, particularly during the time of Polish Pope John Paul II.

But historians estimate that up to 15% of Polish clergy agreed to inform on their colleagues in the communist era.

The Polish Church has launched a series of investigations in recent years to identify collaborators.

Krakow Archbishop Stanislaw Dziwisz, who heads an investigation in his home diocese, said the communist era had been "a time of persecution of the Church, often bloody and brutal".