Gonzo's right, don't quit. Because it sounds very much like they are trying to force you to quit. If the cut in pay is really substantial, say it cuts your pay by more than 25%, say, then you could probably quit and stand a good chance of approval because this is being targeted to force a quit, and they aren't doing it across the board, rather to you as a punishment.
But if they actually fire you, it will be for performance, and in that case, what you say is that you showed up and did your best, and you still were not able to meet their criteria or requirments or quota. That would probably get you approved for benefits easily.
If your gross weekly wage gets down to where it is actually less than you could make on your weekly benefit for unemployment, you could file partial (for part of it) unemployment claims. But that would really be a low wage or significant cut in hours too, probably. If you want to know how much you would qualify to draw, you can go ahead and file a claim while still working, and this will set you up a claim good for one year and "freeze" your wages at your current pay rate.