Neither this part nor any provision thereof, except when specifically so stated, shall apply to commerce with foreign nations or to interstate commerce, except insofar as such application is permitted under the Constitution and laws of the United States; but with reference to passenger stage corporations operating in interstate commerce between any point within this State and any point in any other state or in any foreign nation, the commission may prescribe such reasonable, uniform and nondiscriminatory rules in the interest and aid of public health, security, convenience, and general welfare as, in its opinion, are required by public convenience and necessity.