Airport rail will be put back on the agenda at a debate between Mt Albert by-election candidates tonight.

The proposed rail connection between Auckland Airport and the CBD was a key talking point in last year's local elections and Mt Roskill by-election.

The Public Transport Users Association, which is organising tonight's debate, wants Auckland Transport to reconsider its decision to opt for a light rail connection.

Coordinator Jon Reeves said the candidates will be asked to support an extension to the heavy rail Onehunga Line.

"Aucklanders actually want a fast train to the airport, not a slow light rail service, so will these MPs get behind what the people of Auckland want, or do they have other agendas?"

The Mt Albert by-election is on Saturday. More than 2,000 advance votes have already been cast.