The aviation regulator is expected to decide on Wednesday whether to give the green light to plans to spend about £3.3 billion on planning and early construction for a third runway at Heathrow.
The board of the Civil Aviation Authority is reportedly set to make the decision amid concerns that costs could be passed on to airlines and passengers through higher service charges before the project receives planning permission.
Parliament agreed to back government plans for expansion last year but Heathrow still needs to seek planning approval.
The London hub is due to submit an application for a development consent order, the permit required for nationally significant infrastructure projects.
But Willie Walsh, chief executive of British Airways owner International Airlines Group, told The Times: “With environmental, financial, political and legal hurdles ahead, there’s no guarantee a third runway will ever be built.
“The CAA’s role is to regulate the airport effectively and protect passengers. It’s completely unacceptable for them to expect customers to stump up cash for something that’s not yet got the green light.”
The £14 billion third runway would raise capacity at Heathrow from 80 million passengers a year to more tan 130 million by 2050.
Prime minister Boris Johnson last week raised the possibility that the third runaway project could be shelved.
“Personally, I think that the promoters of the third runway at Heathrow have yet to satisfy the courts, the law, when it comes to our very stringent standards on noise, pollution and air quality,” he told BBC Radio 5 Live.
Shadow chancellor John McDonnell has suggested that Labour could stop the expansion.
A Heathrow spokesman said: “This is a project that will deliver tens of thousands of jobs across the country, connect all of Britain to global growth and will introduce competition between airlines to bring down air fares.
“The CAA must recognise that it is in the consumer and national interest to allow us to deliver Heathrow expansion as quickly as possible.”
The CAA declined to comment.