Your engagement letter is a legally binding contract (both ways).
You need to be careful with other types of contract that it is not constuable as a contract of employment.
If you don't have one you should be able to get an example engagement letter from your supervisory body. Unfortunately, due to the nature of the document it's one of the few things that bookkeepers are adverse to share but if you do a search of the site for engagement letter you should come up with some handy pointers.
kind regards,
Shaun.
__________________
Shaun
Responses are not meant as a substitute for professional advice. Answers are intended as outline only the advice of a qualified professional with access to all relevant information should be sought before acting on any response given.