As per labour reform regulations effective 2016, an offer letter made to a foreign worker becomes legally binding after it is signed by both parties. An offer letter to a foreign worker signed by both parties becomes a legal contract.
Hence, after signing, the employer is not allowed to alter or replace any provisions of the offer letter unless such changes have the consent of both the employer and the employee, are within the scope of law and do not compromise the rights of the employee.
The employer must ensure that the employee has read the offer letter and understood it. If it is proved that a worker did not go through the annexes before signing the labour contract, the employer will be fined AED 20,000 for submitting incorrect data to MoHRE.
If the employee is in the UAE, he must sign the offer letter before the employer can seek MoHRE's preliminary approval for his employment.
Employers must disclose the terms of the offer letter to MoHRE. A copy of the offer letter is stored in the MoHRE's database. Employees are issued work permits based on these offer letters.
(Moreover, it depends on which job offer letter you signed because there are 2 types of offer letter being given by employer, the company internally issued Offer Letter and the MOL Offer Letter. The process usually goes like this, Once you signed the offer letter it will be submitted to MOHRE for job approval, then they will issue the MOL Job Offer Letter. Once you signed the MOL Offer Letter it is now considered as a legal contract therefore both the company and the employer is now legally bounded. If ever they already submitted your job offer letter to the MOHRE and you signed a job offer letter from another company, then it will result to confusion and may proceed to disapproval. You can further request or ask your company regarding their policy on your matter or the details on the job offer you signed.)
For further details please see https://government.ae/en/information-and-services/jobs/employment-process-in-the-private-sector