National MP Sarah Dowie is being investigated by police over a text message she allegedly sent to Jami-Lee Ross, telling him "you deserve to die".
The text was allegedly sent from Ms Dowie's phone to Mr Ross on August 11, 2018, at 1:19am.
Mr Ross has spoken publicly about having a long-term affair with Ms Dowie, which ended mid-2018.
In New Zealand it is illegal to incite or encourage another person to take their own life, punishable by up to three years in prison under the Harmful Digital Communications Act and up to 14 years in prison under the Crimes Act.
Ms Dowie is the MP for Invercargill and is National's Conservation spokesperson. As an electorate MP, it's unlikely she will be stood down from the party.
Mr Ross was sectioned to a mental health unit at Middlemore Hospital last year.
On Tuesday, Mr Ross told Newshub police told him they had received an anonymous complaint through Crimestoppers in relation to the text.
He said he doesn't know who made the call to police and doesn't believe it would be anyone close to him.
"I didn't initiate that complaint but agreed to co-operate."
Mr Ross resigned from the National Party about an hour before the party caucus unanimously voted to expel him in October last year.
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It was one of the most dramatic political moments in recent memory, Mr Ross levelling accusations of corruption against National leader Simon Bridges and Mr Bridges pegging Mr Ross as the leaker of his expenses to Newshub earlier in August.
Police have confirmed they are investigating the text message sent to Mr Ross, but would not comment any further.
Ms Dowie has not replied to Newshub's requests for comment, but it's understood she was not aware police were investigating her.
A spokesperson for National said in a statement: "The National Party is aware of media reports of a police investigation but has not heard from police. If there is an investigation, then we would expect people to cooperate fully."