2017 New York Laws
CPL - Criminal Procedure
Part 2 - The Principal Proceedings
Title J - Prosecution of Indictments in Superior Courts--Plea to Sentence
Article 270 - Jury Trial--Formation and Conduct of Jury
270.30 - Trial Jury; Alternate Jurors.

270.30 Trial jury; alternate jurors.
1.   Immediately after the last trial juror is sworn, the court may in
  its discretion direct the selection of one or more, but  not  more  than
  six additional jurors to be known as "alternate jurors", except that, in
  a  prosecution  under section 125.27 of the penal law, the court may, in
  its discretion, direct the selection of as many alternate jurors as  the
  court  determines  to be appropriate.  Alternate jurors must be drawn in
  the same manner, must have the same qualifications, must be  subject  to
  the  same  examination  and  challenges for cause and must take the same
  oath as the regular jurors. After the jury has  retired  to  deliberate,
  the  court  must  either  (1)  with the consent of the defendant and the
  people, discharge the alternate  jurors  or  (2)  direct  the  alternate
  jurors not to discuss the case and must further direct that they be kept
  separate and apart from the regular jurors.
2.  In  any  prosecution in which the people seek a sentence of death,
  the court shall not discharge the alternate jurors when the jury retires
  to deliberate  upon  its  verdict  and  the  alternate  jurors,  in  the
  discretion  of  the  court,  may be continuously kept together under the
  supervision of an appropriate public servant or servants until such time
  as the jury returns its verdict. If the jury returns a verdict of guilty
  to a charge for which the death penalty may be  imposed,  the  alternate
  jurors  shall  not  be discharged and shall remain available for service
  during  any  separate  sentencing  proceeding  which  may  be  conducted
  pursuant to section 400.27.