GREENS MP Adam Bandt will ''take the temperature'' of Parliament by putting up a motion backing gay marriage in the hope of encouraging supporters to express their true feelings.

This follows the ALP's national Left co-convener Doug Cameron declaring it is ''absolutely crazy'' for Labor, which claimed to be progressive, not to be backing same-sex marriage.

But Senator Cameron got short shrift from Julia Gillard for his call for a loosening of party discipline on this and other issues.

Asked whether there were any circumstances in which she would allow a conscience vote on gay marriage, Ms Gillard said the party had considered the issue at its last national conference.

''We came up with the answer … The party's policies and platform are that the Marriage Act should stay in its current form with marriage being between a man and a woman,'' she said.