Which motivation theory(s) do you think would communicate the importance of vacation time to your employees?

Positive reinforcement would be a good theory for showing how time off can help the employees. Giving a form of coercion or insistence that they take their available time off can help them and the company find ways to more efficiently use the payroll hours at hand as well as maximize the output that employees produce when they are working.

If people cannot talk about policies, they cannot change them.