The thread from a week or so ago about CHAM's weakened signal (since apparently fixed) made me wonder about this and I have to admit I honestly don't know the answer.

Can a radio station licenced to broadcast at, say, 50,000 watts, just decide one day for whatever reason to suddenly lower its output? It's one thing if it's a technical issue with the transmitter or there's some other temporary reason for it. But if a Bell or a Rogers decided they wanted to save money by permanently lowering their power, is that legal? Or would they need some government permission to do it for good?