The ACT opposition says taxpayers will have to foot the bill for the territory's light rail network if there is no Commonwealth investment in the project.
Transport spokesman Alistair Coe accused the government of "changing its story" on how it would fund the network after Chief Minister Katy Gallagher said building Capital Metro was not contingent on federal government or private sector support.
Mr Coe said the government was asking Canberra taxpayers to wear the risk of "light rail at any cost".
It comes two days after an Infrastructure Australia report did not include light rail on its priority projects list and instead suggested buses down Northbourne Avenue.
But Ms Gallagher dismissed Mr Coe's comments, saying it was "entirely reasonable" for a public infrastructure project to be funded through the public purse and "I don't think we've ever suggested otherwise".
The Chief Minister said she did not know what else the government could do to convince Canberrans that it was genuinely committed to seeing the $614 million project through.
"The government's story on light rail seems to be changing," Mr Coe said.
"Initially they said that they were looking at the options and they would do some serious studies.
"They still haven't done the serious studies and yet they have given a firm commitment to Canberrans that they are going to deliver on light rail.
"Now we've heard just yesterday that the project, which is meant to be a public-private partnership, doesn't necessarily need to be a public-private partnership; it can just be a public project."
Mr Coe said Canberrans wanted clarity on where the project was headed.
The Canberra Liberals have not publicly stated whether they support light rail. Mr Coe said on Thursday they would not state their position until they had seen a cost benefit analysis and other evidence to support the project.
"What the government is doing with light rail is reckless," he said.
"They shouldn't be committing to that kind of expenditure before they've done the proper checks and balances."
Ms Gallagher said the ACT needed a rapid transit solution across the city, whether it was light rail or buses.
She said the government had "never ever suggested" that light rail would not be funded through taxpayer dollars.
"If the private sector does partner with us they're not going to fund it out of the goodness of their own heart," she said.
"That's not how public private partnerships work."
Ms Gallagher said the project would still be viable even without Commonwealth funding or support from Infrastructure Australia.