Foreign workers who want to work in the US need a work visa.
To hire foreign workers, employers have to file for a work
permit petition.
Employers don't have to get any documents for workers, neither to assist them;
they have to fill form I-129 (typically "Petition
for A Nonimmigrant Worker"), plus enclose a standard cover
letter. Visa petitioners are subject to fees (around $500).
The form with all instructions can be reviewed and
downloaded
from the INS official
web site