The Council of Trade Unions (CTU) says vulnerable employees will be left working dangerously long hours with no breaks if proposed Government legislation is passed.
The CTU made its submission on the Employment Relations (Rest and Meal Breaks) Amendment Bill at Parliament on Thursday morning
The bill repeals legislated meal and rest breaks, instead requiring employers to provide reasonable breaks where possible and compensation where not.
CTU president Helen Kelly told the select committee hearing submissions that that change removes employees' right to a break and could leave some working dangerously long hours.
She said some will have to agree to their hours of work during the 90-day probationary period, when they can be subject to instant dismissal.
The legislation is disgraceful, Ms Kelly says, and will put workers at risk of exploitation.
The bill is due to be reported back to Parliament for further debate in October.