It would be dangerous to become reliant on that (and many seem to be!) because of course it is never guaranteed and could disappear at any time.
And a good way to guarantee a loss of income is to go on some form of industrial action that involves not working.
If either side works on the basis of assuming service cuts are coming and they then don't, both sides risk a lot of embarrassment and far greater consequences than if they'd done nothing...
But one side will know whether service cuts are coming (and when, and how deep), whereas the other side may not...