The Forward has a report on the top 14 kosher meat producers. It details what they pay, what benefits workers get, and which are unionized.
Here's the breakdown:
Please click to enlarge.
The highest paying company by far is Hebrew National.
One company nicely mentioned in the report is Aurora, which used to be under the supervision, I think, of Rabbi Ahron Soleveitchik. Reb Aharon was always strongly against discrimination and oppression of workers.
Read the entire Forward report.
As Industry Faces Criticism, a Look at How the Kosher Sausage Gets Made".pdf