There's a professor at my school that claims to be writing a book. He is requiring students to sign a non-disclosure agreement (NDA) before certain lectures because he wants to maintain certain ideas of teaching his content part of his intellectual property.
I think that part is reasonable (to an extent) since he is protecting his ideas.
What I think is unreasonable is the fact that he requires all students to sign these NDAs, and offers no alternative presentation of the subject matter. Thus if a student does not wish to sign, they end up missing out on lectures that they have already paid the university to receive, and they have a potential of missing out on graded content that is "covered" by the material that the professor is restricting.
Students have no notice that this will happen prior to entering the class and thus are forced to sign if the don't want to withdraw.