The Mayor and Council may from time to time, on their own adoption or on petition, after public notice and hearing, amend, supplement or change the regulations and districts herein established and adopt rules and regulations for the purpose of interpreting and carrying this chapter into effect. Every such proposed amendment, supplement or change shall be referred by the Mayor and Council to either the Board of Adjustment or any Planning Board which may be legally in existence at that time for the purpose of investigation and report. The recommendation sent to the Mayor and Council shall be advisory only.