Radio Service Bulletin (Bureau of Navgation, U.S. Department of Commerce), February 1, 1922 (No. 58), page 8:

BROADCASTING.

    Because of the rapid development of radio broadcasting during the last three months, the value of such service to the public, and the limitation of wave lengths which can be assigned for this service, it has been found necessary to take precautions to protect the broadcasting service from interference. It was decided first to regulate broadcasting by the larger stations by requiring special authority to do so on special wave lengths. It later became apparent that some restriction must be placed on amateur stations, and the privilege of amateur broadcasting was temporarily withdrawn pending the adoption of a plan which would be acceptable to the amateurs engaged in radiotelegraphic communication.
    Two plans have been suggested: First, the use of 200 meters [1500 kilohertz] between certain hours each day, and, second, the use of the wave length of 175 or 225 meters [1714 or 1333 kilohertz] for broadcasting only. If the second plan is agreed upon with the wave length of 175 meters, this authority could be given in the ordinary amateur licenses. The use of 225 meters will require special licenses.
    The Bureau would like to have any practical suggestions from radio inspectors and amateurs which will be helpful in reaching a satisfactory solution of this question.