LABOR'S official support for gay marriage will cost it the next election, predicts the Australian Christian Lobby, which vowed yesterday to work hard to make sure it happens.

The lobby group will turn to the Coalition to try to ensure it stays committed to its policy on marriage, and gear up for a lobbying campaign next year when a vote is taken, according to managing director Jim Wallace.

Jim Wallace from the Australian Christian Lobby. Credit:Andrew Taylor

Mr Wallace said the group would highlight the differences between Labor and the Coalition on same-sex marriage.

''It seems to me a desire for political suicide. The voters they are trying to get from the left would have come anyway on preferences, and now they have lost the centre.''