Unions have called for ministers to hold an emergency summit about the HS2 rail project following growing speculation about its future.
The Trades Union Congress and five member unions said stakeholders must be brought together “urgently” to get the line “back on track”.
Rising costs have led to speculation that the Birmingham to Manchester leg of the high-speed line will be axed.
On Thursday, Rishi Sunak refused to say whether HS2 will run to the North West.
When asked about the project in a series of interviews for BBC local radio and television stations, the prime minister repeatedly shifted the focus to local bus links and improving roads by fixing potholes.
He said the government was ensuring “we get value for money”.
Earlier this week, the Times reported Mr Sunak has been “alarmed” by the escalating cost of the HS2 project, with suggestions that it could eventually exceed £100bn.
In their statement, the unions argued that cancelling the second leg from Birmingham to Manchester would undermine confidence in the UK’s ability to undertake and complete large scale infrastructure projects.
They say economic benefits must not be squandered, and constant chopping and changing shows disregard for levelling up.
“The UK already trails much of Europe when it comes to high-speed rail infrastructure,” the statement said.
“While the likes of Spain, France and Germany all have extensive high-speed rail networks, the UK has managed just 70 miles worth of track.
“We are being left behind and it’s communities across the North and the Midlands that will pay the price.”
The high-speed rail project is intended to link London, the Midlands and the north of England.
The first part, between west London and Birmingham, is already under construction.
But the scheme has already faced delays, cost increases and cuts. The planned eastern leg between Birmingham and Leeds was axed in late 2021.
TUC general secretary Paul Nowak told the BBC’s Today programme that HS2 was a “key national infrastructure project” and was “too important to be treated as a political football”.
He said a summit was needed to bring together HS2 contractors, unions, regional mayors and the government to discuss how to “get the project back on track”.
Mr Nowak said a way needed to be found that “delivers for taxpayers, but crucially also delivers benefits for UK supply chains, creates and sustains good quality jobs and drives regional economic growth”.
In March, the government announced that building the line between Birmingham and Crewe, and then onto Manchester, would be delayed for at least two years.
The last official estimate on HS2 costs, excluding the cancelled eastern section, added up to about £71bn.
But this was in 2019 prices so it does not account for the rise in costs for materials and wages since then.
In June, a statement to Parliament said £22.5bn had been spent on the London to Birmingham leg so far while £2.3bn had been spent on preparing other sections, on measures such as buying up land.
The possible scrapping of the leg to Manchester has also raised concerns over plans to improve rail services across northern England.
The Northern Powerhouse Rail (NPR) scheme plans to speed up links between Liverpool, Manchester and Leeds through a mixture of new and upgraded lines.
However, these plans include a section of the HS2 line from Manchester Airport to Manchester Piccadilly, as well as planned upgrades to Manchester Piccadilly station.
Earlier this week, the Mayor of Greater Manchester, Andy Burnham, said scrapping the HS2 extension to Manchester risked “ripping the heart” out of the NPR scheme.
