National met an Opposition in full attack mode during debates over the introduction of a 90-day probationary period for new workers.
Labour - which draws many of its MPs from trade union ranks and strongly opposes the measure - stacked its benches with its senior MPs for the first reading of the bill in Parliament yesterday.
The bill will allow businesses with fewer than 20 staff members to put new workers on probation for their first 90 days of work. They can be dismissed without having recourse to a personal grievance for unjustified dismissal.
It will come into effect next April and was an unexpected addition to the raft of measures included in the law changes National is pushing through under urgency before Christmas.
Minister of Labour Kate Wilkinson said the bill would encourage employers to give new workers, including the long-term unemployed, young people and others who struggled to get work, a chance.
"Currently there are no provisions for trial periods in our existing employment legislation. In fact, we are one of the few countries internationally that do not have a trial period for employees."
Under the bill workers will not be able to raise a personal grievance if they are sacked within the 90 days.
However, workers could access complaints processes for discrimination and good faith provisions apply.
"This bill is not about taking away rights, it is about giving opportunities. It has safety mechanisms to ensure that it is fair and balanced and a win-win both for employee and employer."
Ms Wilkinson said beneficiaries who were sacked under the law would not face a stand-down period, there could be no roll-over of the probation period and it was voluntary.
The use of urgency to push through the law - which is not in National's "100-day plan" - was strongly criticised by Labour in Parliament.
Labour leader Phil Goff also criticised National for leaving it until the last minute before releasing the bill, tabling it just before midnight the previous night.
Mr Goff said it stripped Opposition parties of the ability to consider it properly before debating it, and compounded the effects of eliminating the select committee process.
National also met with criticism from its ally the Maori Party, which invoked the "agree to disagree" clauses in its agreement, saying it would oppose the bill because it did not protect workers' rights enough.
Labour's attack was fuelled by the Human Rights Commission call the day before for the Government to allow the bill to go to a select committee, describing it as a "fundamental change" to labour laws and saying there was no need to push it through under urgency.
The bill passed by 63 votes to 55 with National, Act and United Future voting in favour.