Each transit district shall have power to engage in collective bargaining with duly appointed representatives of an employee labor organization and may enter into labor contracts concerning wages, salaries, hours, sick leave, working conditions, collective bargaining and pension or retirement provisions. In case of any labor dispute involving a district and its employees where collective bargaining does not result in agreement, the parties shall submit such dispute to arbitration pursuant to arbitration provisions in any labor contract assumed by the district or entered into by the district, or, in the absence of such provisions, to the Board of Mediation and Arbitration in accordance with the procedure set out in section 31-97, and shall abide by the decision rendered under the provisions of section 31-98. As used in this section, the term “labor dispute” includes, but shall not be restricted to, any controversy between a district and its employees or their representatives concerning terms, tenure or conditions of employment or concerning the association or representation of persons in negotiating, fixing or maintaining, or seeking to negotiate, fix, maintain or change, terms or conditions of employment; and the term “labor organization” means any organization which exists and is constituted for the purpose, in whole or in part, of collective bargaining, or of dealing with employers concerning grievances, terms or conditions of employment, or other mutual aid or protection.