UPDATED 12.35pm: Mike Sabin may have been forced out of Parliament, but it's unlikely National will lose control of his electorate seat.

Mr Sabin has resigned following reports he's the subject of a police investigation, and there'll now be a by-election.

Labour leader Andrew Little accepts National's likely to keep the seat, but says his party will provide voters a choice.

"We polled, I think 16 percent in the party vote in the last election.

"Northland clearly is not a Labour stronghold, but they've got issues out there. They've got unemployment at a rate of 8.6 percent, they've got major problems with housing, which are big issues for us."

MPs are holding a two-day caucus retreat in the Wairarapa, to work on strategies for the political year.

Labour's never held the seat, leader Andrew Little says they'll give it a real crack.

"We know what the prospects are for us, but we think it's important that there is a good message out there in Northland to the voters about what's happening with jobs or not, and what's happening with housing or not.

"And we'll be putting the message out so that Northland voters get to have a choice."

Labour hasn't begun its selection process for a candidate yet, but general secretary Tim Barnett says while the odds are against them, they're hopeful they can make some inroads this election.

"We're realistic about the history of that seat. It has been a bedrock National seat, but also has had strong pockets of Labour support and Labour won quite a number of voting booths in the election last year."