Transportation Act of 1920 upon the Interstate Commerce Commission, and since transferred to the Federal Communications Commission, over accounts and depreciation rates of telephone companies does not, in the absence of exercise by the federal agency of its power, operate to curtail the analogous State authority;[875] nor is an unconstitutional burden laid upon interstate commerce by the action of a State agency in requiring a telephone company to revise its intrastate toll rates so as to conform to rates charged for comparable distances in interstate service.[876] GAS AND ELECTRICITY The business of piping natural gas from one State to another to local distributors which sell it locally to consumers is a branch of interstate commerce which a State may not regulate.[877] Likewise, an order by a State commission fixing rates on electric current generated within the States and sold to a distributor in another State, imposes an unconstitutional burden on interstate commerce, although the regulation of such rates would necessarily benefit local consumers of electricity furnished by the same company.[878] In the absence, on the other hand, of contrary regulation by Congress a State may regulate the sale to consumers in its cities of natural gas produced in and transmitted from another State;[879] nor did Congress, by the National Gas Act of 1938, impose any such contrary regulation.[880] Likewise, a State is left free by the same act to require a gas company engaged in interstate commerce to obtain a certificate of convenience before selling directly to customers in the State.[881] And where a pipe line is used to distribute both gas that is brought in from without the State and gas that is produced and used within the State, and the two are commingled, but their proportionate quantities are known, an order by the State commission directing the gas company to continue supplying gas from the line to a certain community does not burden interstate commerce.[882] The transportation of natural gas from sources outside the State to local consumers in its municipalities ceases to be interstate commerce at the point where it passes from a pressure producing station into local distributing stations, and from that point is subject to State regulation.[883] A State public utilities commission is entitled to require a natural gas distributing company seeking an increase of rates to show the fairness and reasonableness of the rate paid by it to the pipe line company from which it obtains its supplies, both companies being subsidiaries of a third.[884] A State agency may require a company which sells natural gas to local consumers and distributing companies, transporting it in pipe lines from other States, to file contracts, agreements, etc., for sales and deliveries to the distributing companies;[885] nor does the fact that a natural gas pipe line from the place of production to the distributing points in the same State cuts