Some senior Labour MPs say the party has a much harder job on its hands to win back the support of its core traditional voters with the departure of Shane Jones.
The list MP will quit Parliament in a few weeks to take up a role helping Pacific island nations make more money from their fisheries.
MP Damien O'Connor said Mr Jones has been part of a group in Labour that is in touch with the party's traditional voter base.
"A bunch of New Zealanders who sit in the middle, who understand all the core values of the Labour Party but need to see their views represented - and we've just got to work a bit harder to pull them across the line to vote for us in the next election."
Former leader David Shearer said the party needed to focus more on capturing those in the centre, such as blue collar workers, if it was to have any shot at forming the next Government.
Labour leader David Cunliffe said Mr Jones' leaving had nothing to do with the direction of the party or his leadership.
John Tamihere, a former Labour MP, said Shane Jones' decision to quit just a few months before an election beggars belief, and he should have decided on his future after the September poll.
He said the National Party has pulled a masterstroke in removing a top Labour MP at this point in the election cycle.