Call OFAC and ask if any of the matching persons has a US Social Security number.
You can also ask the union to provide you with DOB and address info and see if any of that information is or is not a match on the OFAC list.
Review the FAQ's that OFAC has regarding how to determine if a match is positive or false.http://www.treas.gov/offices/enforcement/ofac/faq/
I am guessing that you are getting hits on names such as Carlos Gonzales, Ceaser Rodgriguez, etc. I was at a bank where we had 5 DIFFERENT Carlos Gonzales's. Fun stuff.