Suspicion, lack of trust, whining and complaining are sure signals that the climate has dropped. If the climate stays low, there is no way you can improve morale because everything looks like a problem to people. When the work climate improves, the petty sniping will just go away on its own. In a more positive environment, a tricky situation is just another thing to handle, not a personal threat. Increased union pressure.
Unions feed on businesses with low climates.
When your staff feels insecure, the union's pitch can seem like a life raft in rough seas. Without dissatisfaction on the job, a union has no product to sell. When you notice symptoms that the climate has slipped a bit, don't panic. When I would encounter whining and complaining on the job, I would take it as just a signal that I had been spending too much time in the office. All I would need to do was pay more attention to the dining room staff or hang out in the kitchen, find out what the crew needed and help them get it.