I wouldn't be so quick to jump to the conclusion that they were _actually_ union. They may very well have been. But companies have a long, proud history of playing VERY dirty tricks in response to unionization.

A former boss of mine once bragged about how he killed a union effort at a previous job. He worked a corporate job for a chain of restaurants that was threatening to unionize. He was given the task of showing up pretending to be a union-affiliated, bafflingly incompetent asshole. He went to individual employees to discuss the "benefits" of joining the union, because in a group he was more likely to be called out by somebody actually union-affiliated.