Opposition Leader Tony Abbott says any national poll on gay marriage should not be held in conjunction with September's federal election.

Independent MP Tony Windsor has swung support behind a plebiscite being held alongside the September 14 federal election to gauge voters' views on gay marriage laws.

The Greens have said it is a distraction and Mr Abbott should allow coalition MPs a conscience vote on legislation before the election.

Speaking during a break in the annual Pollie Pedal in South Australia, Mr Abbott told reporters on Monday the federal election should be "uncomplicated by other matters".

"I think the government and now the independents will want to muddy the waters with other things but the election in September should be a referendum on the carbon tax; it should be a referendum on the current government," Mr Abbott said.

He said if a plebiscite were to be commissioned "it should be held quite separate from a federal election".

AAP pjo/k