applying federal employment tax withholdings against the wages. That works if you have 20 workers who stay on the job for every one who stays at home. If your payroll obligations exceed the withholding taxes you're collecting, then you have to wait for 2021 and receive a tax credit next year to recover your loss.
Keep in mind this only applies to small businesses (under 500 employees). Most small businesses are in one location. If a shelter in place order comes down, the whole company will have to shut down. The owner will be obligated to continue to pay workers with zero income coming through the door. It's a horrible piece of legislation. It sounds good, but it's primary effect is going to be to drive mom and pop businesses into financial ruin.