The Serious Fraud Office (SFO) has launched an investigation over donations made to the Labour Party in 2017.
The SFO is a law enforcement agency tasked with investigating fraud and corruption.
"We consider that making the current announcement is consistent with our past practice in this area of electoral investigations and in the public interest," SFO director Julie Read says.
Labour president Claire Szarbo said in a statement her party hasn't been advised of the specifics, however will "fully cooperate" with any SFO investigations.
"For completeness however, we note that we have already made statements to media in February confirming that two men who were then being investigated by the SFO and had made donations to the National Party, had also made donations to Labour," she said.
"We will not be issuing any further statement while the investigation is underway."
What are the other investigations?
The SFO says it is now carrying out four investigations over electoral funding matters - while a fifth investigation is now before the courts.
New Zealand First Foundation
The SFO's opened a formal investigation into the New Zealand First Foundation donations scandal.
It follows reports last year from Stuff that the New Zealand First Foundation was a slush fund which received more than half-a-million-dollars in donations.
Money was allegedly spent on party expenses like the party HQ, hiring boxer Joseph Parker for a party conference and legal advice for an MP.
Peters has repeatedly denied the claims labelling them "fake news" and "filthy allegations without any proof".
In September 2019 a formal complaint was laid over Auckland Mayor Phil Goff's 2016 election expenses declaration.
It related to the declaration of cash donations from fundraising auctions of $366,115.
Stuff reported the complaint was under section 112D of the Local Electoral Act 2001, 'Filing a false return of electoral donations and expenses'.
A complaint was received by the SFO in February about donations from Christchurch Mayor Lianne Dalziel's supporters during last year's mayoral race.
The Christchurch City Council's electoral officer was asked in December to find out why Dalziel only identified six people who donated over $1500 to her mayoral campaign, Radio New Zealand reported.
They donated through an auction run by Dalziel's husband. Dalziel said she acted on her husband's advice, which was that donors who gave more than $1500 did not need to be declared. She later apologised.
National Party donations
The SFO laid charges against four people in relation to two $100,000 donations to the National Party.
One of those is Botany MP Jami-Lee Ross, who is facing charges which carry a prison term of up to seven years if convicted.
The other three are Zhang Yikun, the wealthy Chinese businessman who allegedly offered a $100,050 donation to National; Colin Zheng, Zhang's business partner and prospective National Party candidate; and Hengjia Zheng.
Court documents released to Newshub revealed the charges related to not one, but two $100,000 donations. One donation was made in 2018 and another made in 2017 when Bill English was National Leader and Prime Minister.
In relation to the 2018 donation, the charging documents detail the SFO's allegations saying, "the defendants adopted a fraudulent device, trick, or stratagem whereby the 2018 donation was split into sums of money less than $15,000, and transferred into the bank accounts of eight different people, before being paid to, and retained by, the National Party".
All four defendants face charges of deception over the 2018 donation.
Ross, Zhang and Colin Zheng face the same charge in relation to the 2017 donation. Hengjia Zheng does not but is also facing a charge of providing misleading information to the SFO.
This trial is scheduled for September 2021.