On Wednesday morning, Treasurer Tim Pallas said the plan to offer a 50-year lease on the public asset would conservatively net up to $6 billion to plow back into productivity-boosting transport infrastructure.

But in apparent attempt to make the deal as attractive as possible, any future government introducing added competition by building a second container port – potentially either at Hastings or on the other side of the bay near Werribee – could be forced to pay compensation to the new operator.

The proceeds of the port's sale will be used to fund the government's two-term commitment to remove 50 level crossings, among other transport promises.

Mr Pallas said the returns from the lease transaction offered an opportunity to significantly boost productivity by putting the proceeds back into transport infrastructure.

"A 50-year lease will allow the leaseholders to plan for the investment needed to maintain and improve the port."

With the Greens against the sale, Labor will need the support of the opposition in the upper house to pass the legislation, risking a multi-billion hit to the bottom line.

Shadow treasurer Michael O'Brien cast doubt on whether the Coalition would support the bill in its current form, accusing Labor of "killing off any prospect" of a second container port for Melbourne for 50 years.

"We had the Port of Hastings being developed alongside the Port of Melbourne, Labor now proposes to effectively kill that off," Mr O'Brien said.

He said the opposition would need to be persuaded that Labor's proposal was in the public interest, raising concerns that the port would run up against space constraints well before 2065.

"There are significant land-lock issues at the Port of Melbourne. There's a limit to how much it can expand," he said.

The Port of Melbourne is Australia's largest container port, visited by more than 3000 ships each year.

The government will remain the landowner and the port will return to the government after 50 years, with an option to extend the lease for an extra 20 years. Annual tariffs will be capped at the consumer price index for at least 15 years.

Mr Pallas said the lease would allow the government to access a 15 per cent bonus under the Commonwealth's asset recycling program in which states can sell assets and reinvest the proceeds in infrastructure projects.

That means if the port sale becomes bogged in the upper house Victoria also stands to lose up to $900 million of federal cash.

But the port sale has also been controversial with rents increasing by about 650 per cent. The Port of Melbourne is currently locked in a legal dispute with stevedore company DP World about the rent hike.

DP World is seeking an undertaking from the Victorian government and port corporation of capped rental charges.

The Australian Logistics Council said the rent increases would affect the future competitiveness of the port. The council's managing director Michael Kilgariff said "excessive rents" would have a detrimental effect across the supply chain.

"Significant increases to port rents will push up the price for users of the port, costs will be passed on to consumers and make it harder for local manufacturers to compete," he said.