Ministers are drawing up plans to take over prisons contracts worth £200m from Carillion, .
Administrators are reported to have been put on standby as talks about the English-based firm's future continue.
"Handing Carillion bosses a blank cheque bail out is completely unacceptable - company bosses should not be rewarded for failure with public money", it said in a statement.
"As part of its engagement with stakeholders, Carillion is in constructive dialogue in relation to additional short term financing while the longer term discussions are continuing".
"It would have major implications for the outsourced government contracts the company holds, as well as the firm's thousands of workers, those in the supply chain and those who rely on Carillion's pension fund". It employs 43,000 people globally.More news: Chris Simms' NFL Divisional Playoff Picks
It also maintains 50,000 homes for the Ministry of Defence, manages almost 900 schools and manages highways and prisons.
A spokeswoman for the government declined to comment to the BBC on any specific meetings.
Scottish Labour's shadow economy secretary Jackie Baillie called on the Scottish Government to clarify the potential impact if Carillion collapses.
He added that workers "should have protection and guarantees from the government, including an assurance that operations will be directly transferred over to Network Rail with all jobs, pensions and rights safeguarded if Carillion goes bust".
Carillion this evening dismissed reports lenders have rejected a critical restructuring plan.
Cabinet Office minister David Lidington hosted the summit of senior figures including Business Secretary Greg Clark and Chief Secretary to the Treasury Liz Truss.More news: James Franco says allegations he's heard aren't accurate
The group - which was demerged for Tarmac in the late 1990s - is a major supplier to the government with contracts across education, the NHS and the rail industry, including HS2. "We are committed to maintaining a healthy supplier market and working closely with our key suppliers".
One of many private companies to run public services in Britain, Carillion is fighting to survive after costly contract delays and a downturn in new business prompted a string of profit warnings and a first-half loss of more than 1 billion pounds ($1.4 billion).
The firm's share price has plunged by more than 90% over the past year.
Carillion is facing a £300m shortfall in funding and met banks on Wednesday to present a business plan, outlining its turnaround pathway.
A TPR spokesperson declined to confirm or deny it was attending any such meetings, but said: "We have been and remain closely involved in discussions with Carillion and the trustees of the pension schemes as this situation has unfolded".
LONDON, Jan 12 (Reuters) - British building and services company Carillion remains in "constructive discussions" with its creditors and suggestions they have rejected its business plan are incorrect, the company said on Friday. "It would be inappropriate for us to comment on any individual contractor's internal financial governance".More news: Meghan Markle's final Instagram posts revealed