From the Adbusters site:
On September 15, Adbusters launched legal action against four of Canada's biggest television broadcasters – CTV, CanWest Global, CBC and CHUM. With prominent civil rights lawyer Clayton Ruby as our lead counsel, we're fighting for the right to buy airtime for our advocacy TV messages, which broadcasters around the world have refused to air.
As they say further down on the page, if they are successful, this will change everything, though I'm not entirely sure at the moment if this is a good thing or not. I'm seeing it more as government increasing its power over broadcasters. I'll be on the lookout for something more from somebody who knows the intricacies of the issue.