Tens of thousands of workers have been sacked under the 90-day-trial period, with many let go because they "did not fit in", news website Stuff reports.
Figures published by the Ministry of Business, Innovation and Employment show about 69,000 employers took on at least one new staff member in 2012 under the legislation.
It is not known how many workers were dismissed during the 90-day-trial period, but the figures revealed 27 per cent of employers said they had fired at least one new employee during or at the end of their trial, the website reports.
This means at least 18,000 people lost their jobs in the first three months of employment last year, with the actual figure likely to be much higher, according to Stuff.
The law has been widely criticised by unions and the Labour Party, which says it will repeal it if it is elected next year.