Unfortunately, you do qualify as an exempt employee, since as a nurse you are considered a 'learned professional,' so you may be payed on an hourly basis or a salaried basis.
See the Department of Labor's website on the topic:
You would also qualify for the managerial/administrative exemption, since your primary duty is to supervise other staff.
As a salaried employee, your salary is not dependent on the number of hours that you work, meaning that if you perform any work in a week, you are entitled to your salary for that week.
However, as an at-will employee, your employer is free to set a schedule for you, even as an exempt employee, requiring that you be at work at certain times, including nights and weekends.
Your employer cannot refuse to pay you, however, if you work any hours during the week. However, your employer would be within its rights to discipline you for missing a shift, up to and including, termination.
I wholeheartedly agree that your situation is unfair and that it is completely illogical for you to not be receiving higher raises as a supervisor compared to other nurses, but unfortunately, your employer is not doing anything illegal in classifying you as a salaried employee.
However, due to your value as a shift supervisor, I highly suggest that you request a higher raise and bonus, possibly with other shift supervisors, since the current system is very unfair while being legal.
That said, since there's no law being violated, an attorney is not going to be able to assist you, unless you want to hire an attorney to negotiate a better salary and benefits package for you.
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