Originally Posted by
raysalmon
It's against the law to require specific documents to prove work authorization. In other words, they cannot ask you for a "green card", they may only ask you to prove you are authorized to work in the U.S. Look at the instructions for completing the I-9 form. Pretty clear on there what the employer's obligations are.
Since Green Card is one of the documents listed on the I-9 form, technically yes, they can ask you for it specifically, particularly if lack thereof might limit the airline's ability to schedule you for some destinations. There have been cases where an unexpired I-551 stamp in one's foreign passport has been accepted as a substitute, but here again, depending on the passport in question, there may be scheduling issues.