Dear
On (date) I was informed that (name of employer) had decided to (include information about decision and/or action by the employer) based on my grievance of (date or period of incident giving rise to grievance) which I raised on (date of first grievance letter) to (person letter sent to).
I would like to appeal against this decision, taking into consideration the following information (include details of your reasons, justification, etc.)
Kindly reply within (---) days from the date of this letter.
Sincerely,