The Labour Party is promising to repeal employment law changes that came into effect on Friday.
Under the changes any new workers - not just those in smaller workplaces - can be put on a 90-day trial, and union access to workplaces will be restricted.
The Government says the changes will make the labour market more flexible, helping both employers and employees.
It argues that extending the 90-day trial period to all workplaces - it had originally just covered firms employing fewer than 20 staff - will particularly help those people who traditionally find it difficult to get work.
But Labour's labour spokesperson, Darien Fenton, has criticised the changes as unfair and unnecessary. She says the trial period change puts workers at risk and denies them justice if they're sacked within 90 days.
Most employers might be fair, Ms Fenton says, but a number will use the new law to take staff on and then sack them for no reason. Nor will the change encourage firms to properly train their new staff, she says.
Minister puzzled by Labour view
Labour Minister Kate Wilkinson says that while the 90-day trial is a matter of choice for workers, it does offer an opportunity to those who otherwise might have difficulty getting work.
She says she finds Labour's view puzzling, as the trial scheme has been in operation for two years and an Institute of Economic Research report on it "basically said it was responsible for up to 13,000 new jobs, and I think that's pretty positive".
Ms Wilkinson says the Government will monitor the new rules and says further changes are possible if any loopholes become apparent.