Police are looking into National MP Sarah Dowie after she allegedly sent a text to former colleague Jami-Lee Ross, telling him he "deserved to die".
Her text was sent in August and Mr Ross claims it caused his mental breakdown two months later.
The Invercargill MP was having an affair with Mr Ross.
Mr Ross said it was not him who lodged the complaint with police.
It is against the law to encourage or incite anyone to commit suicide.