Prime Minister John Key has signalled further changes will be made to employment law if the National-led Government is re-elected in November.
Mr Key has told the Seafood Industry Council conference in Wellington on Wednesday that a more flexible labour market is better for both employers and workers.
He was reluctant to spell out what other changes National might make to employment law, refusing to say whether they include further restrictions on collective bargaining.
But he says that while the changes will be good for employers and workers, trade unions won't be happy.
John Key says the 90-day probation period has been successful in encouraging employers to take on staff, and helped to keep unemployment rates lower than they otherwise would have been.
He says unions will not like the proposed changes, but they will strengthen moves aimed at making it easier for employers to employ people.
But Council of Trade Unions secretary Peter Conway is questioning how successful that has been.
Mr Conway says the changes the Government has already made have not halted a rapid rise in youth unemployment or in long-term unemployment.
The Employers and Manufacturers Association is hoping for changes on collective bargaining and wants the reintroduction of youth rates.
The election will be held on 26 November.
