Holiday request withdrawal to be approved by line manager

When a holiday request has been approved and then the employee changes their mind and no longer wishes to take this holiday, they can currently withdraw the holiday without the need for authorisation from their manager. This can sometimes be very short notice and can turn up to work, in some cases we have already covered their shift so this leaves us with additional staff we do not require. We operate a 24/7 support centre so although an email may be sent to the approving manager that a holiday has been withdrawn they do not always see an email notification at evenings and weekends.