New Zealand First leader Winston Peters has said he will oppose the government's health and safety reforms unless amendments are made to the legislation.

Peters told reporters he lacked confidence in the Bill as drafted. The stance follows a meeting with Pike River campaigners Anna Osborne and Sonya Rockhouse, to whom he gave an undertaking that he would not vote for the reforms if unsatisfied with changes.

Criticism of worksite distinctions

Peters criticised provisions in the Bill that distinguish between different workplace sizes, calling the distinctions highly unsatisfactory and unfit for purpose.

Drawing on his own background, he said: "She's not worked underground, I have. So I've got a bit more better idea than some about what I'm talking about."

Peters said the Pike River disaster, in which 29 people died, occurred because of reduced safety standards. He described the mine as a "corporate manslaughter site" and said that without changes to the Bill, there would be an increased likelihood of another Pike River chapter in New Zealand history.

Peters said he would wait to see developments at the Bill's second reading before making a final decision.

Bill overturns post-Pike River reforms

The Health and Safety at Work Amendment Bill, introduced by Workplace Relations and Safety Minister Brooke van Velden in February, proposes an overhaul of New Zealand's workplace safety framework.

The reforms would undo many provisions of the 2015 Health and Safety at Work Act, legislation enacted following the Pike River explosion.

Van Velden has said consultation with unions, businesses and workers revealed they overwhelmingly felt the law was too complicated and needed simplifying. She has rejected suggestions the Bill would lead to widespread workplace accidents, saying "it is not the case that we're going to see widespread accidents".

Parliamentary battle ahead

The Education and Workforce Select Committee has returned its final report on the Bill, which now awaits its second reading. Labour and the Greens have opposed the legislation.

Osborne and Rockhouse are in Wellington this week seeking to persuade politicians to reject the Bill. Osborne said the government was weakening workplace protections she had worked hard to strengthen, and expressed hope Peters would follow through on his opposition.