Ministers are facing calls to guarantee hospital patients will still be fed if service provider Carillion goes bust.
Shadow health secretary Jon Ashworth said a promise should be given in the next 24 hours that all those affected by the potential collapse will be protected.
He claimed failure to do so would plunge the NHS winter crisis into a new level.
Mr Ashworth said the current situation was "very serious indeed" – as ministers met in Whitehall for crunch talks about Carillion's fate.
Patients deserved "piece of mind", he added, that hospital services such as catering, maintenance and cleaning work would continue even if the contracted firm went into administration.
Carillion, which is Britain's second largest construction group but also operates in schools and hospitals, is on the brink of collapse.
Administrators could be called in within days unless shareholders, creditors or the Government agree to stump up funds, it is believed.
The company has struggled since reporting half-year losses of £1.15bn.
Carillion is currently leading the HS2 construction and other big Government infrastructure projects.
Mr Ashworth urged Health Secretary Jeremy Hunt to come to the House of Commons on Monday and give "clarity" about the situation.
He told Sky News: "I think we do need that clarity from the Government – Monday, I wold say, in the House of Commons.
"But certainly as soon as possible, because the NHS is in a state – we're in a huge winter crisis.
"I've been on Sky umpteen times in recent days, talking about the scale of the crisis in the NHS with people in corridors on trolleys and so on.
"This would be the last thing we need in the NHS if Carillion went under and it impacted on patient care."
TUC deputy general secretary Paul Nowak said vital public services and tens of thousands of jobs were at risk.
"Workers, taxpayers and public service users could well be left to carry the can," he said, warning against a Government bailout.
"Carillion is a textbook example of the failures of privatisation and outsourcing.
"The Government needs to step in, guarantee jobs and services, and explain how they let this mess happen in the first place."
Earlier, new Conservative Party chairman Brandon Lewis told the BBC's Andrew Marr Show: "It is a growing concern.
"It's a very commercially sensitive situation so I wouldn't comment further than to say it is a growing concern.
More from Carillion
"I would hope to see that the working capital they need will be there, working with their partners.
"But of course ministers and my colleague the Secretary of State at Business (Greg Clark) is keeping a very close eye on it."