Winston Peters has launched legal action over the leak of information that he had been overpaid superannuation for seven years.
Papers have been served to four former ministers and two journalists, among others.
In August, the New Zealand First leader said it was unclear how the error in his superannuation overpayment had occurred and he had paid back the money. He did not disclose the amount.
Mr Peters, who is now the deputy prime minister and foreign minister, is seeking a disclosure of documents from numerous former National government ministers, their staff and two journalists.
They include the former Prime Minster and National Party leader Bill English, his deputy Paula Bennett and the senior ministers Steven Joyce and Anne Tolley.
Journalists Lloyd Burr and Tim Murphy are also being served, as is Mr English's former chief of staff Wayne Eagleson and National's campaign press secretary Clark Hennessy.
Ministry of Social Development chief executive Brendan Boyle is also included.
National Party leader Bill English said he was not aware of papers being filed against him by Mr Peters.
Mr English said if they were filed, it would be a legal matter and he would not comment.
A spokesperson for Mr English said members of the National Party named in the papers refuted any suggestion they were involved in the leak and would be "responding accordingly".
Mr Hennessy said he strongly denied any involvement in the matter.
Prime Minister Jacinda Ardern said Mr Peters gave her a heads up at the end of last week that he intended to pursue the matter.
She said she did not have the full details but it was a personal matter for Mr Peters and she would not be making any comment.
- Early 2010: Winston Peters applies for superannuation. He says it was done in the company of his partner and in the presence of a senior Ministry of Social Development (MSD) official. He was not an MP at the time.
- 19 June 2017: Ministry of Social Development chief executive Brendan Boyle is told of Mr Peters' case during a routine briefing on operational matters.
- July: MSD sends Mr Peters a letter notifying him of the incorrect superannuation payments. Mr Peters said he met with an the MSD area manager and the error and overpayment were corrected within 24 hours.
- 27 July: The MSD chief executive is told the matter has been resolved to officials' satisfaction. He then discussed with the State Services Commission if the matter should be disclosed to the minister.
- 31 July: Then-Social Development Minister Anne Tolley is verbally informed by MSD's chief executive about the matter under the 'no-surprises' policy.
- 1 August: Then-State Services Minister Paula Bennett is briefed by State Services Commission.
- 15 August: Ms Tolley is briefed again by MSD that it is satisfied with the outcome of its meeting with Mr Peters.
- 27 August: Mr Peters puts out media release saying that there had been a mistake with his superannuation payments and that the issue had been corrected and resolved.
- 28 August: MSD and Inland Revenue confirm they are investigating whether their departments were involved in the leaking of information to the media.
- 29 August: Ms Tolley and Mrs Bennett confirm they were briefed and the Prime Minister's office says chief of of staff Wayne Eagleson was informed. State Services Commissioner Peter Hughes said ministers were briefed about the issue only after all decisions had been made. Then-Prime Minister Bill English says neither the Beehive nor the National Party had leaked information but it would have been better on this occasion if ministers were not told.
- 12 September: Inland Revenue clears its staff of leaking Winston Peters' personal information. It said it did not hold the information that became public and so could not have been the source.
- 15 September: The Ministry of Social Development and Department of Internal Affairs complete their investigations. Neither investigation found anyone responsible for the leak.
- 7 November: Mr Peters' launches legal action. He is seeking disclosure of documents from numerous former National Government Ministers, their staff and two journalists.