Not even because of workers' rights, but because they simply hate the Orthodox. Stephen Bloom, who started the brouhaha in his book "Postville" bragged how much he hated the Hasidim, that they had no business living in Iowa, and the purpose of his book was to damage their community as much as he could. Even as he got himself invitations to Sabbath meals all over the neighborhood, he was thinking up ways to smear them while he was stuffing his pie hole with their food.
The heck with the people who live in outlying areas where kosher meat was not available before Postville.
Some Modern Orthodox were ‘useful idiots’ to Stephen Bloom’s anti-Hasidic agenda. They were upset at how workers were supposedly treated - “not given soda.”
It is all a bunch of loshen harah, nothing proven. They shamed the community.