The government is being challenged over plans to axe £15m in funding from the National Railway Museum revamp.
Ministers have said they are “minded to withdraw” levelling up investment for certain culture projects, including the NRM masterplan.
But York leaders say without the funding, the NRM’s plan to expand its Great Hall could not go ahead.
It would also see an end to plans to create a public square next to the hall, forming part of the larger York Central development behind the station.
That, too, would be dropped without the government cash.
York and North Yorkshire Mayor David Skaith and the leader of City of York Council, Cllr Claire Douglas, are calling on the government to commit to the original £15m pledge.
They have written to Deputy Prime Minister Angela Rayner to make their views known.
David Skaith said: “The National Railway Museum is the jewel in the crown of Yorkshire museums. This funding is essential both to the museum and the York Central development.
“The York Central designs put NRM at the heart of the development, centred around Museum Square.
“It is an essential part of delivering over 3,000 new homes, 40% of which will be affordable and social rent, contributing to more than 6,000 new jobs and up to £1.6bn in economic value to the region.
“We’re calling on the Government to ensure York and North Yorkshire can unlock this opportunity and provide long-term growth and prosperity.”
Cllr Douglas said: “We want to see funding from the Government confirmed to allow the National Railway Museum to get on with delivering its masterplan.
“This will ensure it builds on its international reputation and help support future growth in York’s visitor economy.
“This is a nationally significant project and a key part of the regeneration of the York Central site.
“It’s vital to the National Railway Museum’s future that it can modernise the visitor experience and attract millions more people through its doors in the years ahead, cementing its status as one of the most visited attractions in the north of England.”
The mayor and Cllr Douglas are to raise the issue at a meeting with the minister for local growth, Alex Norris.
If the funding does come through, construction at the NRM Main Hall would begin this year, with completion scheduled for 2027.