The crisis at Carillion deepened on Friday after reports that lenders had effectively rejected a rescue plan and that two of the Big Four accountancy firms were preparing to act as administrators.
The shares fell by more than 35pc on the news and this afternoon were 19pc down, at 16.15p.
The move does not necessarily mean that EY - which has been acting as an adviser on the company's rescue plan for several months - will ultimately be appointed, according to insiders.
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".
Ministers reportedly discussed the contingency plans in place should Carillion collapse, news of which first emerged on Wednesday during Cabinet Office orals.
Sky News revealed last weekend that Carillion needs hundreds of millions of pounds within weeks to survive. The deficit of that scheme now stands at about £580m.
Unions warn that 19,500 British jobs are at risk if Carillion can't reach a deal with creditors.
"The thousands of workers with Carillion and those in the supply chain servicing its contracts across the public sector will be desperately anxious about the future and they too need to be reassured by the Scottish Government as a matter of urgency".
The rescue plan shown to lenders on Wednesday includes handing back some loss-making contracts, revising the terms of others and potentially accepting financial support from the Government if it can not secure it from private sector sources.
So far, numerous banks have indicated that they are reluctant to provide additional funding given the potential for huge losses on their existing exposure.
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A Government spokeswoman said: "As Carillion is a major supplier to Government it should come as no surprise that we are carefully monitoring the situation while working to ensure our contingency plans are robust".
Its only asset sale since the crisis erupted has been to offload a portfolio of healthcare contracts to rival outsourcer Serco for £50m - against a broader forecast for disposal proceeds of £300m.
Carillion, a facilities management and construction services company, has struggled since reporting half-year losses of £1.15 billion, and a meeting is being held to discuss its pensions deficit.
Notably, it holds a contract to build part of the forthcoming HS2 high speed railway line and is the second largest supplier of maintenance services to Network Rail.
It is also engaged in building the Aberdeen Bypass and was responsible for constructing the Tate Modern art gallery in London and the Channel Tunnel.
Earlier in January, Carillion also discovered it was under scrutiny from the UK Financial Conduct Authority regarding "timeliness and content" of it financial statements leading up to its July 2017 profit warning.
Since then, the company has cleared out its executive team, including chief executive Richard Howson and finance director Zafar Khan.
Carillion's fight for survival is being led by interim boss and industry veteran Keith Cochrane, a former CEO of engineer Weir Group.
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".