Alien Registration Number

[asingh15]

Hello

I am working H1B in USA on contract for an federal client. Now for security purpose and verification they want to know my Alien Registration Number. I checked on my I797 form, there no Alien Registration No. I know these number start with A#.

Do I really need Alien Registration No? As I know Alien Registration No is available to green card holder and US Citizen.

Please advise

 

Thanks

[ashuneel]

A# is issued at I-140 approval stage. For dependents it is issued at I-485  receipt notice.