Governing bodies of counties, cities, or other local governmental units, when authorized by the Department of Commerce and Economic Opportunity, may cooperate with the governing bodies of the counties and cities or other governing bodies of any adjoining state or states in the creation of a joint planning commission where such cooperation has been authorized by law by the adjoining state or states. Such a joint planning commission may be designated to be a regional or metropolitan planning commission and shall have powers, duties and functions as authorized by “An Act to provide for regional planning and for the creation, organization and powers of regional planning commissions”, approved June 25, 1929, as heretofore or hereafter amended, and, as agreed among the governing bodies. Such a planning commission shall be a legal entity for all purposes.