Here is article 60 of UAE's Labour Law concerning the wages of employees.
No amount of money may be deducted from a worker's remuneration in respect of private claims, except in the following cases;
a) the recovery of advances or amount of money paid to the worker in excess of his entitlements, on condition that the amount deducted in this case not exceed 10 per cent of his periodic remuneration;
b) contributions which the worker is required by law to pay from his remuneration, eg. towards social security and insurance schemes;
c) the workers contributions to a saving fund or repayment of advances repayable thereto;
d) contributions towards any welfare scheme or in respect of any other privileges or services provided by the employer and approved by the labour department;
e) fines imposed upon the worker for any offense he has committed;
f) any debt payable in execution of the judgment of a court of law;
Provided that the deduction shall not exceed one-quarter of the workers remuneration. Where two or more debts are payable, the maximum shall be half the workers remuneration and the sums of money attached shall be divided pro rata among the beneficiaries, after payment of any legal alimony at the rate of one-quarter of the workers remuneration.
Xavier can complain to the Ministry of Labour and Social Affairs if the company continues to deduct his salary.