Carillion shares plunged on Friday following reports that lenders had rejected a proposed rescue plan for the business.
Shares dived this lunchtime to as little as 12.97p - valuing the company at just £55.8m - after it was reported EY had been selected by Carillion's directors to be on standby for an administration.
Carillion also said turnaround proposals on the table were likely to cost shareholders.
It comes as the government, pension authorities and stakeholders meet on Friday in an attempt to thrash out a rescue package for the firm that would help it avoid collapse.
It has been awarded contracts to build part of £56bn High Speed 2 railway, including the first phase of the line which will run between London and Birmingham and is scheduled to open in 2026.
It also maintains 50,000 homes for the Ministry of Defence, manages almost 900 schools and manages highways and prisons.
In a note to clients, Peel Hunt's analysts said: "We suspect that given its mounting liabilities, recent press comment, growing customer worries and supply chain hesitancy that Carillion will be forced (by the banks) to accelerate its financial restructuring".
A government spokeswoman said it has been monitoring the situation to ensure its "contingency plans are robust".
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 also manages almost 900 schools, provides services to the NHS and works with National Grid.
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The government is being urged to bring contracts from Carillion back into public control amid fears the struggling construction giant could "collapse".
Ministers have held crisis talks over a troubled company that hundreds of schools rely on for vital services, after questions were raised about its future.
The Pensions Regulator would not comment on whether it was attending specific meetings, but a spokesman said: "We have been and remain closely involved in discussions with Carillion and the trustees of the pension schemes as this situation has unfolded".
However, no announcement has been made on a business plan to secure its future.
On Thursday, ministers overseeing everything from justice to transport, health and education met to discuss how they should respond to the possible demise of a company that plays a central role in British public life.
Cabinet Office minister David Lidington hosted the summit of senior figures including Business Secretary Greg Clark and Chief Secretary to the Treasury Liz Truss. "We are committed to maintaining a healthy supplier market and work closely with our key suppliers", she said.
Carillion is a major supplier to the Government and has contracts in the rail industry, education and NHS.
Carillion's share price has fallen by more than 70% since the middle of 2017. "It would be inappropriate for us to comment on any individual contractor's internal financial governance".