Wikipedia
New Zealanders speak colloquially of party-hopping as waka-jumping when a Member of Parliament (MP) switches political party between elections, taking their parliamentary seat with them and potentially upsetting electoral proportionality in the Parliament of New Zealand.
The imminent advent of MMP in New Zealand parliamentary politics in the 1990s — culminating in its use from the 1996 election onwards — led to a series of defections and re-alignments as the old monolithic two-party system broke up and many politicians struggled to define and project their images and beliefs in new parties and groupings. The new political climate tended to favour the establishment of new political parties (whereas in former times dissidents had often simply become independent MPs). Voters tended to punish waka-jumpers in this period, but some survived and flourished, often to the disgust of their former party colleagues. Due to the frequency of waka-jumping, New Zealand enacted legislation (the Electoral Integrity Act of 2001, expired at the 2005 election) which required any MP who had entered parliament via a party list to resign from Parliament if they left that party's parliamentary caucus. As the actions of the Progressive Party in 2002 showed, parties still found ways around such law.