Collective bargaining under chapter 164, Laws of 2006 may not be for the purposes of making a collective bargaining agreement take effect before July 1, 2007. No party may engage in collective bargaining under chapter 164, Laws of 2006 to amend a collective bargaining agreement in effect on March 21, 2006. A collective bargaining agreement or amendment thereto entered into under chapter 164, Laws of 2006 shall not be effective before July 1, 2007, and may not have any retroactive effect.