Acting Prime Minister Winston Peters is expected to take the stand at the High Court in Auckland today, as his privacy lawsuit against former National ministers kicks off.
The New Zealand First leader claims his privacy was breached ahead of the 2017 election, leading to details of his superannuation overpayment being made public.
Mr Peters repaid up to $18,000 after being notified by the Ministry of Social Development (MSD) and then issued a press release after receiving questions from reporters.
He's now pursuing legal action against National MPs Paula Bennett and Anne Tolley, as well as the Attorney-General David Parker on behalf of MSD, the ministry boss Brendan Boyle and the State Services Commissioner Peter Hughes.
The ministry had notified Ms Tolley - as its responsible minister - about Mr Peters' case after it was resolved. Mr Hughes also informed his minister, Mrs Bennett.
Mr Peters argues they never should have advised the National MPs, as it increased the risk of the details leaking to media and hurting his reputation and election chances.
Early court documents revealed Mr Peters was pursuing $450,000 each in damages from three of the defendants, and another $450,000 from the remaining two. Any damages awarded would be covered by the taxpayer.
Mr Peters' lawyer is expected to lay out his case this morning before the MP takes the stand to give evidence and then be cross-examined.
Mrs Bennett and Ms Tolley could appear as early as Wednesday or Thursday. The hearing is set down for three weeks.
As is usual custom, Mr Peters - who is Deputy Prime Minister - will act in Jacinda Ardern's role while she is in Thailand for the East Asia Summit.
Due to the High Court action, however, Labour deputy Kelvin Davis will chair Monday's Cabinet meeting in Wellington.