Formal invitations to events, weddings and parties dictate a formal reply in return, whether you are accepting or declining the invitation. It makes the event planning significantly easier for the host to receive a response from everyone; sending a note to decline helps clarify head counts.
Check the box next to the "decline" option on the response card if provided.
Write a short note if no response card is provided. This can also be included even if a response card is provided on an additional piece of stationery..
Begin the note formally and in the third person, echoing the way the host addressed the invitation to you. For example, write; "Ms. Jessica Smith regrets that she must decline your kind invitation."
Include the reason why you cannot attend. For example, "Ms. Jessica Smith regrets that she has a prior commitment on that date and must decline your kind invitation."
Close with good wishes for the event. For example, write; "Wishing you the best of luck on your special day."