A co-manager said be careful how many times you call the union. What the hell?
I would ask the manager to explain that one in front of my union steward. Sounds like a threat to me. In fact, I think you should call the union and report it!!!
Yes, they know how often the union is called, because the union rep will be coming to them for inquiries.
As for whether they know WHO called the union, I dunno. I'm not familiar with how the union handles reports and grievances, or if there's an option for anonymity.
It's "nice" way of saying "stop reporting the shady ****. I warn you. Or so help me, I'll in inconspicuously make your career at Kroger a nightmare, made sure to NOT look like harassment."
I would report it to your union. They CANNOT prevent you from doing so