WALD leases its lines from Sprint. Several years ago, there was an organizing campaign at a Spanish-language subsidiary of Sprint in San Francisco. The company shut down, fired all the workers, etc. and there was a massive unfair labor practice case, which I think we won.
When I signed up with WALD, I asked the person on the phone if they were union and he said they were (not that he'd be motivated to lie for my subscription!). I never dug too far to determine the truth but sort of pursued a don't ask, don't tell policy.
Personally, I think it's pretty much a wash, morally speaking. WALD does donate the money to some good organizations, not just the usual liberal groups.