你要的法律條文 I-9 表上一抬頭大黑框“反歧視注意事項”裏就有。

"Employer CANNOT specify which document(s) they will accept from an employee. The refusal to hire an individual because of a future expiration date may also constitute illegal discrimination."

鏈接
http://www.uscis.gov/files/form/i-9.pdf