That’s the question posed to Fr. Z., who offers this response:

I think the pastor does have a certain measure of control over what you preach. He is the pastor, even if he is an heterodox jackass. The pastor, parish priest, parochus, is responsible for preaching in the parish.

For example, the pastor can determine that you are going to preach about topic X on Sunday Y. As a young priest I went back to my home parish in the USA for the summer. Sometimes the pastor had a project for preaching. For example, he divided up the Cathechism of the Catholic Church and every Sunday all the priests had to integrate the designated paragraphs. There are times when the bishop will designate a topic for preaching.

Also, turn the question around and look at it from the other point of view.

Consider your question in the light of a solid orthodox pastor who has an assistant who is a heretic or an idiot. After hearing a few bizarre and doctrinally questionable sermons, the pastor reasonably would have to exercise oversight. I know a case where a priest in residence was absolutely going to the zoo when in the pulpit, not because he was heterodox, but because he wasn’t especially bright. The pastor wanted to check his sermons for content before he preached so as to save everyone some problems.

That said, no one can require you to say anything that is demonstrably contrary to defined teachings of our Faith. Use the Catechism of the Catholic Church as a reference.

Read the rest for context. It’s an interesting problem — one, thankfully, I’ve never had to contend with.