I would imagine they would listen when service levels are so poor that we lose customers. Both of these things are already happening in my area as a result of staffing at the hubs, ramps, and stations. Poor service leads to lost customers and shareholder disatisfaction, and management doesn't get their bonuses.
It is in management's best interest to keep employees happy. Common sense for us, but we all know this company comes to bad conclusions and makes some terrible decisions regardless.
I can say that I know an ops manager recently went to our MD with concerns regarding pay. Nothing has been done (yet?), but at least I know the issue has been brought up. Sadly, I don't think our Senior has the same respect for the employees. I would imagine he's just coasting to retirement based on how he acts towards us.