No electric transmission lines or related facilities shall be constructed by any Federal agency outside the Pacific Northwest for the purpose of transmitting electric energy between the Pacific Northwest and Pacific Southwest, nor shall any arrangement for transmission capacity be executed by any Federal agency for the purpose of financing such lines and related facilities to be constructed by non-Federal entities, except those lines and facilities recommended for Federal construction in the Report of the Secretary of the Interior submitted to Congress on June 24, 1964, as supplemented on July 27, 1964, or as hereafter specifically authorized by Congress: Provided, That, except with respect to electric transmission lines and related facilities for the purpose of transmitting electric energy between the two regions above mentioned, nothing herein shall be construed as expanding or diminishing in any way the present authority of the Secretary of Energy to construct transmission lines to market power and energy.