The Permanent Council of the Bishops' Conference declared on Thursday evening in Czestochowa that it was concerned about the Ministry of Education's plans.
Changes to the subject of religion should only be made after consultation and in agreement with the churches, the bishops demanded.
Education Minister Barbara Nowacka wants to reduce the number of lessons in the elective subject of religion. She said that one lesson a week would be enough.
There are currently two lessons.
The centre-left government formed in December has already decided that the religion grade will no longer play a role in calculating the average grade.
Church will not change its clear position
The bishops are confident that the talks between church representatives and the Ministry of Education will be positive, according to the current communiqué. It does not mention any specific points of criticism.
The Catholic Church had previously pointed out that religious education is anchored in the concordat, i.e. the agreement between the state and the church.
The Permanent Council also opposed the "growing pressure in the public sphere" and government plans to legally authorise "the killing of children in the womb".
It announced a separate message on this subject, which is to be read out in all churches on 12 May.
The Church will not change its clear position, it said.
Poland currently has one of the most restrictive abortion laws in Europe.
Abortions are only permitted if the woman's health is at risk or after a rape.
The governing coalition is planning a liberalisation, but is not in agreement as to how far it should go.