There are a few things you can do to limit your employees.
1. "Shift Offers"- Employees can offer shifts, it's up to Managers to approve.
-You can set the "Privileges" of each type of employee. (Manager,Supervisor, Crew)
- Whether or not and who can approve shifts.
2. Shift Limitations- You can set employees' Max Hours. In the employee "General Info" screen, Enable the ACA then set the maximum amount of hours. Alerts will be sent to all parties involved when they over this amount.