The church has published "To Plagiarize or Not to Plagiarize," a guide that provides sermon-writing tips while warning priests about the consequences of stealing intellectual property.

Father Wieslaw Przyczyna of the Pontifical Academy of Theology in Krakow is one of the authors of the guide. He said the worst offenders are generally young, inexperienced priests who discover on Saturday night that they have no idea what to say at mass the next day.

"Unfortunately the practice has become more usual than not," he said. "But if a priest takes another priest's words and presents them as his own without saying where he got them from, this is unethical and against the rules of authorship."

The church plans to begin spot checks to look for plagiarism and to encourage parishioners to compare what they hear in the pulpit with sermons available online.