So, in general, an employee is entitled to overtime for all hours worked in excess of 40 per week unless their job duties qualify them for an exemption from overtime. This is true even for salaried employees. In the case no exemption applies, the salary is just presumed to compensate them for 40 hours and everything worked beyond that must be paid in addition.
If you are properly classified as an exempt employee, there is no limit to the number of hours your employer can force you to work for the same flat rate salary. Indeed, this is the very purpose of salaried exempt positions--the employee is paid a flat rate to "get the job done," whatever that job may be as determined by the employer.
Based on what you have described, it seems that the administrative exemption may apply to your employment. Here is a summary of the requirements for the administrative exemption. If you believe that this exemption does not apply to you, there is a chance that you are improperly classified as exempt and thus entitled to additional compensation. But it is important to also note that even if you are not exempt, your employer still retains discretion over your schedule and can require you to work any number of hours. It's just that the hours over 40 must be compensated beyond your salary.
If you believe you are owed unpaid overtime, your remedy is to file a wage claim with the NC Department of Labor, which you can do here.
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