IFM wants to combine its $7 billion with $5 billion each from Canberra and Victoria. This money would fund a dedicated airport rail line from Southern Cross Station – which IFM owns and operates – to Melbourne Airport. The plan would include a new six-kilometre tunnel under the city’s inner west. But the state government is unlikely to back the plan, concerned both that IFM’s proposal could cost dramatically more than promised, and at what one Labor MP referred to as the “Transurbanisation” of Melbourne’s rail system. Under its plan, IFM would own the tunnel for four decades and charge access fees to the state to recover its investment. The state government wants to use the funding from Canberra, first offered by Malcolm Turnbull in 2018, to build new rail tracks between the airport and Sunshine.

Loading Airport trains would then run via the Metro Tunnel rail loop under central Melbourne, now under construction. The Metro Tunnel, originally budgeted at $11 billion, was justified by a promise to dramatically increase services to Melbourne’s west. The possibility IFM’s bid will be rejected has angered both Wyndham and Geelong councils, which would have benefited from the new dedicated tracks into Melbourne Airport. Wyndham mayor Josh Gilligan said the state government was happy to dump contaminated soil from the West Gate Tunnel in the city’s west, but not give it better transport options by allowing dedicated airport rail track from the city centre to be built. “We are worth more than cheap and quick decisions about prisons, and contaminated waste. We should be getting the best transport options and choices that delivers the best connectivity within our city and between Geelong, Werribee and Melbourne,” he said.

Loading Geelong mayor Stephanie Asher has also said places like the west of Melbourne and Geelong were "taking the bulk of the population growth with little to no transport infrastructure”. The state opposition infrastructure spokesman, David Davis, said a key reason the government did not want to proceed with the market-led bid was that it needed the federal money to help bail out the Metro Tunnel. That project is in crisis, running well over budget for the consortium building it, Cross Yarra Partnership. But the state government on Saturday rejected the claim by Mr Davis that money from Canberra for an airport rail line could be used to balance the books on Metro Tunnel. “The contribution from the Commonwealth is to build a Melbourne Airport Rail and that’s exactly what it will be spent on,” a government spokeswoman said.

Loading Federal Cities and Urban Infrastructure Minister Alan Tudge said the $5 billion the Morrison government had allocated towards construction of an airport rail link “is for that purpose only”. The state opposition’s Mr Davis said there was a serious risk, though, that the money could ultimately be used to “bail out or backfill the Metro Tunnel cost blowout”. Public Transport Users Association spokesman Daniel Bowen said the most important part of building an airport rail line was getting it started. “If the airport train depends on having a brand new tunnel serving it from day one, we will still be talking about doing it in a decade,” Mr Bowen said. “And if the West Gate Tunnel has shown us anything, it’s that tunnelling in the inner west is really challenging.”