Unions say potential changes to employment law have been made worse and now breach the right to freedom of expression.
The Employment Relations Amendment Bill could mean employers can walk away from negotiations with staff, and new employees won't be covered by a collective contract when first starting a job.
A select committee has since recommended docking employees 10 per cent of their wages for partial strike action, including breaking an employment agreement or refusing to wear a uniform.
Council of Trade Unions president Helen Kelly says this could be interpreted as wearing a badge objecting to the industrial position of their employer.
The amendments, which have been described as moderate by Labour Minister Simon Bridges, could be passed next year.
