The predominant form of arbitration in labor matters is grievance arbitration, also known as rights arbitration. In grievance arbitration the parties present the arbitrator with a dispute involving the terms of an existing collective bargaining agreement. The arbitrator’s role is to decide the dispute by applying the terms of the agreement.
Another type is interest arbitration, which is used to resolve an impasse or deadlock during bargaining over the formation of a contract or one of its provisions. In interest arbitration the parties ask the arbitrator to settle differences that have led to an impasse in negotiations.
For a concise and helpful discussion about the differences between grievance and interest arbitration see Barry Winograd, An Introduction to The History of Interest Arbitration in the United States, Labor Law Journal, Fall 2010, pp. 164-168.