A former MP says New Zealand First needs to clear up questions about the relationship between the party, and its foundation.

The Electoral Commission is looking into whether the party has been filtering undeclared donations through a foundation in the same name.

Brian Henry, who's behind the foundation, is threatening to sue National leader Simon Bridges and MP Nick Smith over comments said in the House.

Former United Future leader Peter Dunne told Tim Dower the party has some questions to answer.

"The problem has emerged because the explanations have been murky and vague and not entirely clear and down the line, so they have immediately raised suspicion."

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