AGSEM, the TA union here at McGill voted overwhelmingly (79% in favor) to authorize strike action in their ongoing contract negotiations with the University. Obviously, with only a week and a half to go in the semester, this is a point where a strike might be highly effective. Still, since the union has to give 7 days notice (I believe), the window for a strike is fairly narrow. If we get through the next week or so without hearing that a strike is happening, then I would guess there won't be one--a strike that doesn't start until the middle of finals period has only marginal leverage. Therefore, I presume (hope) AGSEM is right on the verge of a breakthrough with the administration. Strike authorization should be enough to tip the scale by itself, and if it doesn't, then the union leadership has to be willing to move very quickly and decisively.
UPDATE: Never mind on the 7 day notice. I have just heard that this is not required. That makes the situation much more flexible. The union could declare a strike anytime before the first couple days of the finals period and have a pretty big stick. We've got up to two weeks of pins-and-needles.