Can an employer place an employee in a new position and not pay the employee for their new role?

Indiana- I was hired in as an order entry clerk, but have been trained from day one to work as a planner. I have been in this position for almost a year now and they have yet to compensate me for it. I have asked countless times and nothing has come of it. My job performance review should be around my 1st year anniversary of August 20th. This is the longest I will wait and if they decide to not compensate me for my role, I have already informed them that I will begin doing the work that I am being paid to do and nothing further.

Is this something that I can do? Can the employer continue having me do work that I am not being paid to do?