IN WHAT is believed to be a first for a Labor-affiliated union, the Australian Services Union has polled its members to gauge their views on same-sex marriage in a move the union plans to extend to other critical issues such as the carbon tax.

More than 70 per cent of the 2100 ASU members polled supported gay marriage, and 23 per cent opposed it.

The union's NSW secretary, Sally McManus, said the ballot gave members a say in national Labor policy and results of future polls would form union policy positions. She said it was a first for a Labor union.

Ms McManus said the result of the same-sex marriage poll would be taken to Labor's national conference in December. ''Normally for controversial issues there would be a committee of about 50 people deciding our position but we decided that because it is now so easy to reach our members with technology, we wanted direct democracy,'' she said.

''We had such a good return rate that we will do this on other issues like the carbon tax, but only once we feel our members have a full understanding of the issue otherwise you would really just be doing an opinion poll.''