If your wish to stop your employee's from being unavailable on a specific day, you can block unavailability one your roster.
1. Open your schedule
2. Click on the day from your schedule
3. Tick the check box to Block Unavailabilities for that day.
Once selected and you click off the window daily stats window, employees will not be able to submit unavailability for that day.
The unavailability block will show on your schedule as per below
