A thousand union members from across Christchurch attended a stop work meeting on Thursday morning against the Employment Relations Amendment Bill.
The rally was organised by the Council of Trade Unions which says the bill would drive wages down and strip workers of their rights.
It followed similar ones in Auckland and Wellington and an oral submission from the Council of Trade Unions to the select committee considering the bill.
CTU president Helen Kelly said the change is designed to humiliate working people and will result in lower wages, no tea breaks and greater workplace vulnerability.
Workers spoken to at the meeting said the changes were as significant as the 1991 Employment Contracts Act.
The law change would allow employers to walk away from negotiations on a collective contract and in some cases ban strikes.