It may be useful to have an investigatory or conciliatory process for these complaints. Allowing them in an adjudicatory process requires substantial thought and planning. It is easier to restrict adjudicatory processes to individual complaints. In investigatory processes, the essential characteristic of an ombudsman is credibility to both the employee and management. If this happens, you may violate the National Labor Relations Act.
Mediation is a recognized professional skill for which training is available.
Although there is no certification requirement in most states, some states, like Massachusetts, have laws that accord a privilege to mediators who have completed training. It is prudent that the training credentials be met. That way, if mediation fails, the mediator is out of subsequent discovery processes. The choice between inside and outside mediators is strongly influenced by the degree to which the insider is perceived as neutral to the dispute. Depending on the organization, adjudicatory steps can be hierarchical beginning with a department manager, then a division manager, and then a company officer.