Background Check - Reference Checks

Dear Professionals,
Seeking your consent in making employment verifications and personal reference checks of the incumbents. What is the best suitable time for making such checks against an incumbent? Is there any legal formality as per UAE labor law ? Is it during hiring process or better to do after hiring with a prior intimation to the candidate in case of failure. Please suggest.
Regards,

Dear Friend,
Reference check is done to get the verification done about the candidate.
In our Company, the reference check is done before issuing the offer letter with any of the previous organization the candidate has worked for and the second reference check is done after the the candidate joins but before issuing the appointment letter with the employer he was working prior joining our Company.
Sometimes reference check is done after intimating the candidate.