Forcing employees to sign a non-competition agreement upon resignation

Hi,

I have been working in a free zone company for almost four years now. For the last six months, my salary was very irregular and I am receiving it around 25th of the next month. My issue is that I have decided to resign and move to another company.

However, I heard that my company is now asking all the employees who are resigning to sign a non-competition document. This document states that we shall not work with any competitor for three years, even though this clause is not mentioned in my employment contract.

Since I am working in a technical company and with my experience, I will only be able to find another job with a company which will be in one way or another a competitor.

Is this legal? Can the company force me to sign the non-competition document?

What will I do if they refuse to give my salary, end of service benefits and experience letter when I resign?