I think you mean who will protect the interests of the consumer? That's ultimately who loses to unions. There's no direct ethical value in protecting businesses or their owners but workers and consumers include pretty much all humans and their interests are in tension with each other.
mostly the government because the consumer has a lot of democratic power.
product regulations and antitrust as examples
I mean if that is your measure, then consumers lose more to capital than organized labor.
Consumers have a choice of not buying, so generally they do not lose to unions.