New Zealand First has decided to exercise the proxy vote of former National MP Jami-lee Ross while he is away from Parliament.

The party has issued a statement saying it had received a letter from Ross asking the party to exercise his proxy vote and indicated it had agreed to do it with reluctance.

"The New Zealand First caucus strongly believes that in terms of the Electoral Integrity Amendment Act, that someone in Mr Ross' position should resign his seat and test his mandate with the electors of Botany and we urge him to do so.

"That said, after careful deliberation New Zealand First is able to confirm that it has accepted Mr Ross' request.

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"The party wishes to make clear that its decision to accept Mr Ross' proxy, until such time as he revokes it, is done solely on the grounds that the electors of Botany gave a clear expression of their will at the 2017 General Election when they elected him with a significant majority."

Speaking to media this afternoon, New Zealand First leader Winston Peters said the National Party should use the waka-jumping law and "get down off its high horse".

"We are here to say to the people of Botany ... 'you deserve to have your voice heard'," Peters said.

Peters said taking Ross' proxy vote and casting it with the National Party helped to preserve the parliamentary proportionality that the voters wanted.

Peters said he had not spoken to Ross.

NZ First would start casting Ross' proxy vote in the first sitting week following the next parliamentary recess.

Ross is on medical leave after having a breakdown.

He was expelled by the National Party after evidence pointed to him being the leaker of the travel expenses of leader Simon Bridges.

Jami-Lee Ross also made allegations of corruption against Bridges over donations to the National Party which Ross collected and he made a complaint to the police.

The New Zealand First statement says it will cast Jami-Lee Ross' the vote at all times in support of the way National votes "as a temporary delegate for the electors of Botany."

"New Zealand First does this to ensure that all New Zealand voters continue to receive representation in Parliament."

Ross this afternoon tweeted: "While I remain on leave on medical advice, it is important my constituents in the Botany Electorate continue to have a vote cast on their behalf in Parliament. I appreciate NZ First supporting Botany by accepting my request to cast a proxy vote."

When Ross was expelled from the National caucus on October 16 he said he would resign from Parliament on October 20 and fight a byelection in Botany. He said he was well enough to resume work.

But he changed his mind on October 20 and said he would stay on as an independent MP – he has resumed his sick leave.

Jam-Lee has tweeted that he appreciates New Zealand First accepting his proxy.