Striking Rockgas workers in Auckland protested outside the office of National MP Jami-Lee Ross against his bill allowing the use of strike breakers on Tuesday.
The bill repeals part of the Employment Relations Act 2000, which prevents an employer using volunteers, contractors or other casual employees during a strike or lockout.
About 40 people marched on Mr Ross's office, chanting for greater worker rights. However, he was not there as Parliament is sitting in Wellington.
The FIRST union says Rockgas workers are striking against low wages, long hours and difficult working conditions and the proposed bill removes the bargaining power of striking workers.
The workers are four weeks into an eight-week strike.
Jami-Lee Ross said unions have a democratic right to protest against his bill which he says won't affect employees' right to strike but will reduce the impact of long drawn-out strikes on companies and their customers.