The Nothing Compares 2 U hitmaker is a vocal advocate of a full investigation into allegations widespread child abuse was covered up by church officials, and she is frustrated other stars have not also spoken out about the scandal.
She has singled out U2 frontman Bono for criticism, accusing him of thanking God for his good fortune but failing to join a "pitched battle" to defend His honour.
O'Connor tells Uncut magazine, "For the representatives of Jesus Christ to stand up and say lies in the presence of the Holy Spirit, lies about the rape of small boys and girls, is a blasphemy against the Holy Spirit, which is unforgivable.
"I get sick of all these rock stars - like Bono - thanking God for their Grammys, but when there's a pitched battle for the honour of God, there's tumbleweed."
Just weeks ago, O'Connor joined Bono and fellow Irish star Glen Hansard to busk for shoppers in Dublin on Christmas Eve (24Dec12).