The decision on whether to build an M4 relief road should not be taken by outgoing first minister Carwyn Jones, a Labour AM has said.
Jenny Rathbone, who opposes the plans, said he should not "tie the hands" of his successor.
Mark Drakeford, Vaughan Gething and Eluned Morgan are competing to succeed Mr Jones as leader of Welsh Labour when he steps down next month.
The Welsh Government said officials were preparing advice for ministers.
Both Mr Gething and Ms Morgan support building a relief road, while Mr Drakeford is thought to be more sceptical.
Jenny Rathbone, a supporter of Mark Drakeford, said: "I don't see how he (Carwyn Jones) can tie the hands of his successor with such a major project.
"I think instead the government should be working hard on how we're going to bring in better public transport both in the short and the long term," she said.
"He's still the first minister until 10 December but I do think it's very odd that he should take such a major strategic decision which is going to tie up so many aspects of our restricted budgets just when he's standing down."
Government officials are currently analysing the report produced by a public inquiry into the planned relief road.
The government's favoured route - known as the "black route" - would see a 14 mile stretch of motorway built to the south of Newport.
The decision will be taken once officials have prepared advice based on the report.
Ministers have said there will then be a vote in the assembly.
Labour's 2016 election manifesto made a commitment to build a relief road around Newport, but did not state which route.
Mr Jones has previously said he will take the decision, although the building of the road would need to be backed in future budget decisions too.
AMs were initially told they would vote on the project in the Senedd on 4 December, but ministers now say they cannot schedule the vote until advice from officials is ready.
Government sources said they were still working towards that date.
Carwyn Jones's successor is due to take over on 12 December.
Other Labour AMs, including Mike Hedges, agree with Jenny Rathbone that the decision should be taken by the next first minister.
And a Welsh Labour source said "around half" the Labour assembly group feel the same.
Wales Live asked the three leadership candidates whether they think Mr Jones should take the decision.
Only Eluned Morgan gave a direct answer, saying she is "happy for the current FM to make the decision".
A Welsh Government spokeswoman said: "Welsh Government officials have now received the inspectors report on the M4 Corridor around Newport project and are in the process of preparing advice for ministers."