2006 New York Code - Retention.

 
    §  756-c.  Retention.  By  mutual agreement of the relevant parties an
  owner may retain a reasonable amount of the contract sum as retainage. A
  contractor or subcontractor may also  retain  a  reasonable  amount  for
  retainage  so  long  as the amount does not exceed the actual percentage
  retained by the owner. Retainage shall be released by the owner  to  the
  contractor  no  later  than  thirty days after the final approval of the
  work under a construction contract. In the event that an owner fails  to
  release  retainage  as  required  by  this article, or the contractor or
  subcontractor fails to release a proportionate amount  of  retainage  to
  the  relevant  parties  after  receipt  of retainage from the owner, the
  owner, contractor, or subcontractor,  as  the  case  may  be,  shall  be
  subject  to the payment of interest at the rate of one percent per month
  on the date retention was due and owing.