Fears the £500m revamp of Ely junction could be shunted into the sidings have grown - after a transport minister highlighted the "significant" cost.
There have long been calls for improvements to the junction so more freight and passenger services can run through what is currently a bottleneck on the rail network.
But concerns over whether the government will pump millions into improving it have been growing, since a transport minister said some projects would have to be "cancelled or indefinitely paused".
A group of 21 MPs, peers, business groups, council leaders and rail freight representatives recently wrote to the government to commit to investment in junctions at Ely and Haughley, near Stowmarket, in Suffolk.
Prime minister Liz Truss, who, as South West Norfolk MP, has campaigned for the improvements in the past, previously said a transport secretary in her government would "look closely" at the project.
But when James Wild, Conservative North West Norfolk MP, raised the issue in parliament, another transport minister made reference to the cost - and how travel patterns have changed following the coronavirus pandemic.
Mr Wild said: "The project is backed by MPs across the east of England because it would increase capacity by 30pc, enabling more passenger and freight services and delivering a major boost to growth.
"Given the overwhelming economic benefits that it offers, will the government ensure that this much-delayed project, for which the prime minister has been campaigning for more than a decade, is now fast-tracked and moves to the next phase?"
Transport minister Kevin Foster said Mr Wild was a "strong champion for the Ely scheme and I recognise the potential for the benefits that he highlighted".
But he added: "It is, though, worth noting that the scheme would require significant public funding with a total cost of up to £500m, so we need to consider that as part of reviewing patterns of rail travel post the pandemic.
"We will therefore seek to provide as much clarity as possible when we publish an update to the rail network enhancements pipeline."
Mr Wild said the scheme's benefit-cost ratio gives a return of £4.89 in benefits for every pound invested, which he described as a "very healthy number" compared to other rail projects.
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