A grant to extend Birmingham Airport's runway will only be paid if the government part funds the diversion of a road at the site, the owners say.
Planning permission was granted in April to extend the runway by 400m to help cater for more long-haul flights.
The airport had secured £25m from a regional development agency to help finance the £120m runway extension.
The firm said it has now been told the £25m depends on the government agreeing to part fund the diversion of the A45.
Diverting the trunk road would add extra time to drivers' journeys and do nothing to ease congestion.
Birmingham International Airport will have to put its case to the government to decide whether tax payers money should be used to fund the highways project to help a private company.
Advantage West Midlands (AWM) offered the money towards the runway in 2007.
Mick Laverty, from AWM, said "I won't pretend it's easy to get the money into an airport project, these are heavily scrutinised projects and airport investment is scrutinised more than most investment."
He said the money was available though and, subject to the business case stacking up, "we will make that investment".
Birmingham Chamber of Commerce said the runway expansion was vital for businesses in the region and would help to create 600 construction jobs.
Jeremy Blackett, from the chamber, said if the extension did not happen "we would no longer have an aspiration to be a global business city, we might as well right that off".
Paul Kehoe, from Birmingham International Airport, said: "We've got planning permission, the 400m can be built.
"What we now need is the political will to deliver the cash to do so."
Stourbridge MP, Lynda Waltho, Labour deputy minister for the West Midlands, said: "The political will has always been there, it still is. Ian Austin (minister for the West Midlands) is waiting with his briefcase open ready to take the case up to Whitehall. All that needs to happen now is a worked up proposal needs to be given to him."