i don't know what your workplace is like or your coworkers, but if they're just normal americans with no familiarity or instilled antipathy toward unions/communism then i would probably pull back a bit on the class war rhetoric. i would focus almost entirely on the concrete benefits they will personally enjoy from union membership, then use that as a bridge to discuss the sociopolitical aspects once the union is implemented.
i feel like most americans will reject the medicine unless you wrap in a slice of cheese first. either way, good luck!