is it lawful to deduct from the salary of an...

We would like to inform you that in accordance with the UAE Labor Law, this is considered a legal violation with the existence of the employment contract and its validity as in the provisions of the law in Article (36):
that the contract determines the date of signing it and the start date and its type and period and the wage.
Therefore, it is not legally permissible to deduct from your salary and you may go to the Labor Office and file the complaint and explain the matter in detail. In case the complaint has been proven, you may claim all your employment rights according to the terms of the contract, and then leave the work according to:
Article (121):
A worker may leave work without notice in one of the following cases:
1- If the employer violates his obligations before the worker in the articles stipulated in the contract or the law.
2- If the employer or his legal representative signs an assault on the worker.