Maybe things are different in the States. When I was in college and taking a course the syllabus for that course was our contract with the prof. It detailed what we could expect for a workload in the course, how things would be graded, that sort of thing.
If this part of the course isn't anywhere in the syllabus and the prof has sprung it on the class then I feel that all of you need to make the prof aware that this is unacceptable. Sure you can grumble about it but nothing will change. Grumble to the right people, at the very least the prof will have to put it in the syllabus and next years students will have a better understanding of what is expected.
There also is your opportunity to express your views with the instructor evaluations. I know its at the end of the term but those things can be devastating for profs.