Documents in secret police files show that about a dozen bishops still alive had ties to Poland’s communist-era secret services, a Catholic Church commission said Wednesday.

But a top bishop warned that the documents may not be an accurate guide on how much the bishops cooperated.

Poland’s Catholic bishops asked the special church commission to review their communist- era files in January, after a scandal in which Archbishop Stanislaw Wielgus of Warsaw resigned just before his installation over disclosures he had cooperated with the former secret police.

Other prominent clergy have also resigned over similar allegations. The revelations have forced the church, revered in Poland for its resistance to the communists, to confront an issue believed to have compromised a minority of clergy.