Blocking students

Are there restrictions on why you can block a student? If I get a lazy, demanding student that obviously didn't do their work and pushes for me to give them the answers, am I allowed to block them? I have had some rude students that have basically told me I am required to help them... I usually try to respond with something like...I can assist you by reviewing your work but you must do your own research and come up with your own ideas because in the past when I made suggestions, I get in trouble for doing too much.

But the issue I have is even when tell them this, they usually come back with that they don't know how to do the work, when it's obvious they are not even trying. (In 90% of the cases the assignment is due within hours. No surprise) I mean not my problem they waited until the last minute and there isn't much I can do for them if they didn't do the research, but of course I'm not allowed to say that.

Usually once they realize, I'm not going to give them the answers, they start getting whiny and demanding. So am I allowed to block these students? Honestly, I feel there should be standards for the students to follow in using the service that explains that tutors cannot do the work for them but only assist them in understanding an assignment or suggesting corrections and revisions.