Labour leader Andrew Little has accused the Government of entrenching zero hour contracts in law, after it proposed changes to the Employment Standards Bill.
Mr Little said the Government had broken its promise to ban zero hour contracts, and its new rules on how employers can use them, which are muddled and confusing, would make little difference to vulnerable workers.
Zero hour contracts require workers to be available for work, but without any guaranteed hours of work.
Workplace and Safety Minister Michael Woodhouse said the contracts were unfair and proposed law changes would give workers more rights.
He said new rules would make it illegal for employers to require workers with no guaranteed hours to always be available for work.
Instead, he said workers would be free to seek work elsewhere to augment their pay.
"It's really hard to ban all of the contracts that are described as that [zero hour contracts]. What we have done is we have prohibited the worst types of behaviour we've seen in those contracts that are described as zero hours," he said.
The law change will not require employers to offer guaranteed working hours, but Mr Woodhouse said the change would incentivise employers to do so.
"Clearly, the employers are going to want greater levels of confidence that they're going to be able to roster the shfits that are available and that's why I believe this will result in better, more certain rostering practices."
But the Council of Trade Unions says the proposed law changes will do nothing but codify what is already a problem and the proposed changes will not force employers to guarantee hours every week.
Council of Trade Unions president Helen Kelly said workers had been promised the contracts would be banned completely, not put into law.
Ms Kelly said the Government had failed to explain why an employer should not be forced to guarantee hours of work to their employees, most of whom work every day.
However Business New Zealand says the Government's on the right track with the new laws affecting zero hour contracts.
Its Chief Executive Phil O'Reilly said everyone wanted regulations, but there was still a need for casual work contracts.
Mr O'Reilly said a highly structured labour market would only lead to higher youth unemployment, less productivity and a less competitive economy.
The law changes would also make it illegal for employers to make unreasonable deductions from workers' wages.
This last provision was sparked by cases where petrol station attendants had their pay docked to cover losses when motorists drove off without paying.
The changes would be included in an Employment Standards Bill, which will be introduced to Parliament later this year.