I have been acting supervisor for a year now and I believe I have more then proven I am capable for the position. The issue is that there is no position available and my team headcount has been shrinking. It is now essential that I perform routine tasks while scheduling and coordinating tasks for the rest of my team, which has caused me increased stress. There is also no hope of the "acting" being removed anytime soon so I would like to step down. Can they force me to continue as acting supervisor?
Can they force me to continue as acting supervisor?
No. Slavery has been abolished. If your real question is "Is my employer required to find a different role for me if I no longer want to be acting supervisor but wish to continue being employed by my current employer?" then the answer is no (though they might consider it).
It's been done many times. The main problem is that it makes future prospects of advancement harder to achieve. You get labeled as not management material, or fails under pressure. Particularly if you remain with the company.
But short term your immediate risk is that they just demote you out the door.