It's a special resolution which means it needs a 75 percent vote in favour at a general meeting and it would have to be registered. It would also need a 75 percent vote to rescind, otherwise it sits there in perpetuity.
Rehardging Whale's comment about how effective (or not) it is, I think it will only work with enthusiastic marketting of the discount and aggressive enforcement of the penalties for late payment. Between paying early and paying late, that's a 20 percent difference in your levies. If that doesn't get their attention nothing will.