It seems to be based on injury rate data submitted to OSHA in three categories ("Lost Time", "Light Duty", "Other"). That's fairly simplistic, so I'm not seeing where the union had opportunities to present the data in an unfair way. The comparison to WalMart, for example, seems straightforward.

I do agree that some of the charts based on surveying workers might be biased, but that's the least interesting numbers in the report.