Particularly in the 1990s, repeated instances of party switching led to criticisms that the proportionality of parliament as determined at a general election had been disturbed.

The Electoral (Integrity) Amendment Acts were therefore attempts by the legislature to control its members' affiliations and votes in a way that conformed to the most recent election outcome.

"[1] The Acts operate differently depending on whether the expelled member represents an electoral district or if they were elected on a party list.

Deputy leader Michael Cullen introduced legislation to forcibly expel party switching members in October 1997, but a 5–5 split on the electoral law committee prevented the bill from progressing further.

Members of Parliament will, therefore, be reminded of the obligations they have to the people of New Zealand when they seek and gain election under the banner of a political party.

"[10]: 78  Anderton, now deputy prime minister, addressed dissonance between his departure from Labour while remaining in parliament and his support for legislation that triggered compulsory expulsions, saying his was "a decision made in a totally different constitutional environment" to Kopu's.

[11] The government worked with New Zealand First, which had also been subject to many defections in the previous parliament, to address these shortcomings and secure that party's ongoing support.

[13] The bill began its second reading on 9 November 2000, before the deal with New Zealand First had been completed, when National whip Gerry Brownlee won the consent of Parliament to have it promoted up the order paper.

[15] Speaking in the debate, Green co-leader Rod Donald addressed New Zealand First leader Winston Peters' apparent change of heart by quoting one of Peters' old press releases: in 1996 he had said "Members of Parliament joining New Zealand First or any other political party without resigning and seeking a new mandate is consistent with constitutional precedent.

[15]: 999 The Electoral (Integrity) Amendment Act 2001 came into force on 22 December 2001, the second anniversary of its introduction and the day after it received the Royal assent.

National leader Bill English called the arrangement deceitful; Anderton denied accusations of waka-jumping because he still supported the government.

[20] ACT attempted to expel list MP Donna Awatere Huata in 2003; after a 10-month legal battle the Supreme Court declared in 2004 Awatere Huata had "distorted, and is likely to continue to distort, the proportionality of political party representation in Parliament as determined at the last general election" and permitted her expulsion to proceed.

[34] Te Tai Tokerau MP Hone Harawira resigned from the Māori Party and Parliament in 2011, forcing and winning a by-election under the new Mana Movement.

[35] There were also three expulsions: Taito Phillip Field (2007)[36] and Chris Carter (2010)[37] were expelled from Labour and Brendan Horan (2012)[38] from New Zealand First.

A 2013 public opinion poll found, that 76% of New Zealanders opposed list MPs staying in Parliament if they leave their party.

[41] Justice minister Andrew Little was responsible for the new legislation and brought papers to Cabinet in 2017 seeking agreement on the policy for the bill and, soon after, for its introduction.

"[45][46] A party spokesperson said the team negotiating the agreement with Labour "forgot" to register the Greens' opposition to waka-jumping legislation because New Zealand First had not explicitly campaigned on it at the election.

[47] With National and ACT, the only other parties in parliament, opposed to the bill, the government relied on Green votes for the legislation to proceed.

That day was, coincidentally, the date of a special debate acknowledging the death of the former deputy prime minister and electoral integrity champion Jim Anderton, whose past contribution to the issue was noted by the current deputy prime minister and New Zealand First leader Winston Peters.

[46] The Bill passed its first reading along party lines with 63 in favour (Labour, New Zealand First, and the Greens) and 57 opposed (National and ACT).

[52] The remaining 40 submitters—including former National MP Lockwood Smith, blogger David Farrar, former Green MP Keith Locke, Annette Hamblett, activist Maire Leadbeater, and the National Party—opposed the Bill on the grounds that it constricted the freedom of MPs to dissent from their parties and the executive.

"[3] Nineteen professors of constitutional and electoral law, including Elizabeth McLeay and Claudia Geiringer, collectively submitted that the bill is legislation in search of a problem.

[53] Ultimately the committee was evenly divided between government and non-government members and could not agree on any amendments to the bill, returning it to the House unchanged for its second reading.

[59] The bill, now sponsored by Nick Smith, was voted down at its second reading 65 (Labour) to 55 (National, Green, ACT, and Te Pāti Māori).

On principle, because of his party's recent opposition to the bill, National leader Simon Bridges declined to write to the Speaker to initiate Ross's expulsion.

[62] National declined to exercise a proxy vote on behalf of Ross; New Zealand First accepted this instead and cast it in line with the votes of the National Party "to maintain 'the democratic right of expression'" and to ensure that Ross was not acting "in a way that has distorted, and is likely to continue to distort, the proportionality of political party representation in Parliament as determined at the last general election," as required by the Act.

He sat as an independent for two months and resigned from Parliament that October, saying he feared that Labour would invoke the Electoral (Integrity) Amendment Act against him.

[73][74] Law professor Andrew Geddis described this apparent loophole as likely Whaitiri advising she had removed her proxy vote from Labour and requested to sit apart from them, rather than officially changing parties.

Following a request by the Green Party, House Speaker Gerry Brownlee expelled independent MP Darleen Tana from parliament.