The wife of a United Future candidate killed at Pike River is urging Peter Dunne to oppose the Government's "watered down" health and safety changes.

Milton Osborne, who died in the coal mine explosion in 2010, stood for Mr Dunne's party in the West Coast-Tasman seat in the 2005 election.

His wife Anna said today that the United Future leader should honour Milton's memory and "oppose the watering down of health and safety laws".

She said Mr Dunne was in a unique position to influence the legislation, which is being debated in Parliament this afternoon.

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"I want Peter Dunne to show the same loyalty to my husband that my husband showed him and their party's values," Mrs Osborne said.

"One of those values was that all lives matter. I am deeply disappointed Dunne has accepted that some workers should have less say over their lives and safety."

Mr Dunne agreed to support the legislation today after negotiations with National.

On his way into Parliament, he rejected claims the bill had been diluted, saying that it had in fact been strengthened. The definition of high-risk industries was now "far more comprehensive and far more effective".

Under the legislation, workplaces with fewer than 20 employees were not required to have a health and safety representative unless they were deemed "high-risk".

Newly-released criteria, which took into account deaths and injuries since 2008, showed most farms will not be considered high-risk.

Mrs Osborne said the Government's definition of high-risk was based on an arbitrary cut-off date. "But there is nothing arbitrary about a death for a grieving family."

She also took aim at Prime Minister John Key, saying he had broken a promise to fix health and safety laws and had succumbed to pressure from agricultural lobbyists.

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The health and safety law changes stemmed from the Pike River Royal Commission. Several of the Pike River victims' families have travelled to Wellington for the final stages of the legislation this week.