Whenever the public necessity, convenience, general welfare or good zoning practice require, Council may, by ordinance, after reference to and recommendations thereon by the Planning Commission, and subject to the procedure provided otherwise in this article, amend, supplement or change the regulations, district boundaries, or classifications of property, now or hereafter established by this Zoning Ordinance or amendments thereof. It shall be the duty of the Planning Commission to submit its recommendations regarding petitions for amendments or supplements.