Prime Minister John Key rejects a claim by an employment lawyer that workers have fewer rights than murderers under the 90-day trial period.
The Government is to extend the scheme to all workers. The scheme has been available for the past year in smaller companies.
Lawyer Max Whitehead, says the law is draconian and unreasonable and effectively murderers have more rights to a fair trial.
But Mr Key told Morning Report that was ridiculous, given that workers can choose to opt out of the 90-day trial period and half of those in a survey by the Department of Labour, had chosen to do so.
He said the law has been operating successfully in small companies with fewer human resources facilities - and thus arguably less likely to follow the law.
Mr Key is adamant that workers have nothing to fear from changes to labour laws.
He announced the changes at the National Party's annual conference in Auckland on Sunday.
He said some people will be sacked within the 90 days, but more will benefit from getting a job.
Mr Key said migrants will have better opportunities to get jobs as employers will be encouraged to take a chance on them.
He said his pizza delivery man, a migrant, told him on Saturday night that he wants a chance to get another job.
However, the Service & Food Workers Union says the changes will create a climate of fear and stifle productivity.
Mr Whitehead told Morning Report up to 50 people have contacted him after being dismissed under the law.
He said they often get emails at home telling them not to go in to work anymore and are not given an explanation.
Equal Opportunities Commissioner Judy McGregor says "the jury is still out" on whether the 90 day probation law creates jobs.
However, Dr McGregor says she would rather see the Government taking action to create new jobs.
She says it is unfair that the current scheme allows employers to fire staff without providing an explanation and that workers have no legal ability to challenge that.