It's a tie between vacation/sick time and health insurance.
Management disciplining employees when required, equal treatment, promoting from within, and removing the "buddy system" when promoting.
Poor management practices and no possibility for promotion. But promotion would be worthless because workcenter supervisors make less then qualified maintainers and earn less vacation.
Fairness and equal treatment of employees, promoting from within, and when they do promote from within, use qualifications and seniority and not the buddy system.
For shift workers, ending the war between shifts. Also supervisors that doesn't partake in the "shift war" and for supervisors to treat employees equally regardless of background.