The precipitating event was Israel's attack on Islamic University in Gaza, which Israel claims is Hamas-linked. Personally, that wouldn't be enough on its own in my view to make it a legitimate target, though if the university was being used to store weapons or was a sanctuary for terrorists (neither of which is particularly unlikely), that would be a different matter. As is per usual, the lack of knowledge of the relevant facts isn't stopping anyone from going insane:
"Attacking an institution of learning is just beyond the pale," CUPE Ontario president Sid Ryan said last night. "They deliberately targeted an institution of learning. That's what the Nazis did."
Now, I'm no history major, but I'm pretty sure the Nazis did a few other things that are the primary basis of their historical condemnation -- though it wouldn't surprise me if Mr. Ryan found those activities to be a lot less worthy of his attention (UPDATE: Fair is fair: Mr. Ryan has apologized for the Nazi comparison, though he has not backed down his original demand for the boycott).
In any event, the academic boycott movement had previously been waged primarily in the UK -- it is not a positive sign that it has hopped the pond to Canada. This "ban", particularly", is especially repugnant to academic freedom, as it prohibits Israeli professors from doing any work in Ontario unless they agree to espouse a particular position -- for many, on a topic that is far outside their area of expertise (what does a Chemistry Professor know about the complex array of military, humanitarian, moral, and legal considerations that should all form a part of our individual judgment of the Gaza operation?).