Section 57-A A steam or electric railroad corporation having a franchise from this state, operating to and from stations within a city of over a million inhabitants, and owned, controlled or operated by a railroad corporation having a franchise from another state, shall not charge a rate per mile within such city in excess of the rates charged for similar service from such city to stations in an adjacent state, by such railroad corporation having a franchise from another state, whether over its own tracks or under an agreement with another railroad corporation