Yes, they may do this: employers have the discretion to approve or disapprove usage of any form of paid time off or comp time. Accordingly, your employer may legally tell you that this is a good time for you to use your comp time, and conversely, could tell you that usage might not be approved at other times of year. They have to let you use your comp time, but your employer actually has much discretion in *when* you use it as you do, though most employers do not exercise that discretion.