Each of us owns our own “business.” We own the hours of our own lives, and our services and skills. An employer RENTS a portion of them from us. They are renters, not owners.
It is not for a renter to unilaterally dictate to the owner how many hours the owner must rent. That decision must be agreed upon by both. If your employer is demanding more hours or services than you're willing to rent them, remember that you're the owner. You get to decide. Not the renter.