N.Y.C. Charter § 43: Section 43. Special meetings.

The mayor may at any time call special meetings of the council. He shall also call a special meeting when a requisition for that purpose signed by five council members has been presented to him. Not less than one day before a special meeting is held, notice of the time thereof and of the business proposed to be transacted, signed by the mayor, shall be published in the City Record, and at the same time the city clerk shall cause a copy of such notice to be left at or sent by post to the usual place of abode or of business of each council member; but want of service of a notice upon any council member shall not affect the validity of the meeting. No business shall be transacted at such special meetings other than that specified in the notice relating thereto.