Labour says it will weed out members of the National Party's youth wing and affiliates who may have tried to switch sides this week in a light-hearted attempt to influence Labour's leadership vote.
Members of National's youth wing were urged to become members of the Labour Party before the Thursday cut-off by right-wing bloggers David Farrar (Kiwiblog) and Cathy Odgers (Cactus Kate).
It is not known how many registered in total. Labour's general secretary, Tim Barnett, said "hundreds, not thousands" of people had applied to become members before the midnight deadline for taking part in the vote on September 15.
Non-members were enticed by the low cost of membership - first-time members could join by paying a koha. Labour recommended a donation of between $5 and $20 but would accept $1. Mr Barnett said all applicants had to declare that they were not a member of another party, because being so was a breach of Labour's rules.
Ms Odgers said on Twitter that she wanted to join Labour so she could vote for MP David Cunliffe to win the leadership: "He represents ambitious, successful, white middle class achievers unpopular with peers."
