A Labor Senator has declared the party will be a "sell-out" if it overturns the ban on uranium sales to India.

Prime Minister Julia Gillard wants next month's ALP conference to change its long-standing opposition to selling uranium to India.

Members of the Labor left are fiercely opposed to the idea of exporting uranium to India, which has not signed the Nuclear Non-Proliferation Treaty, and have vowed to fight it.

More than 100 delegates from Labor's left faction are meeting in Canberra today to discuss issues including gay marriage and uranium.

Labor Senator Doug Cameron told Channel Ten the left will not give in on anything yet.

"On selling uranium to India I think it's a breach of the [Nuclear] Non-Proliferation Treaty and is a sell-out for everything we've stood for as a party over the last 40 years," he said.

But Defence Minister Stephen Smith defended the change in policy.

"If India signs up a separate standard bilateral arrangement with Australia on nuclear safeguards, then there's no reason why we shouldn't export uranium to India," he said.

"If we can export uranium to China and Russia, we can export uranium to the largest democracy in the world. There is no evidence whatsoever of proliferation of nuclear materials."

Senator Cameron says the party's left faction will also keep fighting for same-sex marriage as Ms Gillard pushes for a conscience vote on the issue.

"We're not giving in on anything yet," Senator Cameron said.

"I'm sure the conference today will take some principled positions to say that we should fight for marriage equality, that that's a Labor principle that all Australians should be treated the same."