If any action or proceeding be brought in any court upon any issue or controversy referable to arbitration under a written provision in any collective bargaining contract or under an agreement in writing for submission to arbitration of an existing controversy arising out of such collective bargaining contract, the court in which such action or proceeding is pending, upon being satisfied that the issue involved in such action or proceeding is thus referable to arbitration, shall on application of one of the parties stay the trial of the action or proceeding until such arbitration has been had in accordance with the terms of the collective bargaining contract or the written agreement for submission to arbitration, provided the applicant for the stay is not in default in proceeding with such arbitration.