Deputy Labor leader Richard Marles says the coalition government needs to agree if constitutional recognition for indigenous Australians is to be achieved.
Mr Marles says Labor supports such recognition for indigenous Australians, but are unable to offer up bipartisanship support to the Morrison government as no position has been put forward.
In a speech this week Indigenous Australians Minister Ken Wyatt committed to holding a referendum on constitutional recognition within the next three years.
But since then his colleagues have been vocal on the issue, with some conservative coalition MPs concerned an indigenous advisory body could become a "third chamber" of federal parliament.
One MP has threatened to campaign on the "no" side of a referendum.
"As much as I would love to have optimism about this, the fact of the government's own internal divisions doesn't deliver a lot of that optimism for me," Mr Marles told Sky News on Sunday.
"So before we get to a question of bipartisanship between Labor and Liberal on this question, we actually need to see the government work out its own internals and come to a position itself."
Treasurer Josh Frydenberg, who described himself as a "constitutional conservative", said the government needed to move forward carefully.
He remains unsure if an indigenous voice to parliament would be described as a "third chamber" of parliament.
"What we haven't got is the full detail on that. What we do need now is the process to have a discussion to work out what the model is," he told ABC's Insiders program.
"We've got the right people in charge but we do know that constitutional reform is very difficult."
Australian Associated Press