It is all of them, believe me.
Purdue is no different.
I taught some adult education classes (ESL, reading, GED) at a meatpacker and at a furniture builder in the Chicago areas a few years back. Outside of a few blacks, there were almost no non-Latinos working on the line. I am not going to guess how many were not here legally.
I used to be a supervisor in a biotech company and was involved in hiring. For some reason, I had the responsibility of getting the documentations from new hires to establish their legal status to work in the U.S. I don’t know how Tyson, Perdue, etc. get away with cutting corners on that requirement, except they must have friends in high places.