Outsourcing giant Interserve faces a crunch vote on Friday over its proposed rescue plan.
If shareholders fail to back the debt-for-equity deal, the firm could go into administration by the weekend.
The firm employs 65,000 staff worldwide, 45,000 in the UK, cleaning schools and hospitals, running probation services and building roads and bridges.
Interserve has said the company "is in a critical financial situation".
It accumulated debt after construction project delays and a failed energy-from-waste project in Derby and Glasgow and hopes shareholders will agree to the strategy, although it would dilute shareholders' holdings.
Attention focused on Interserve's financial situation after fellow contracting and construction giant Carillion collapsed in January last year with debts of £1.5bn.
Following Carillion's collapse, the government launched a pilot of so-called "living wills" for contractors, designed to ensure that if companies fail, other contractors are ready to step in to fulfill contracts. Interserve is one of five suppliers taking part.
What is in the rescue plan?
The proposed rescue plan involves cutting the firm's debts from nearly £650m to £275m.
Interserve would issue new shares which it would give to its creditors in exchange for debt.
That would hand lenders the lion's share of the firm, and existing shareholders would be left with heavily watered-down shareholdings totalling just 5% of the firm's worth.
"Our plan preserves some value for shareholders. This will not be the case if the proposals are voted down," the firm said.
What if shareholders don't approve the plan?
Interserve's largest shareholder, Coltrane Asset Management, has opposed the proposed rescue.
The New York-based hedge fund has been pushing for an alternative deal whereby a smaller proportion of the firm goes to lenders, and shareholders retain a larger holding.
If no rescue plan is approved the company is likely to go into a pre-pack administration, which would wipe out shareholders entirely but allow the firm to keep operating.
A pre-pack administration lets a company sell itself, or its assets, as a going concern, without affecting the operation of the business. Administrators take over the running of the business to protect creditors and shareholders lose their investments.
What is Interserve?
The outsourcing firm is one of the UK's largest public services providers. The firm started in dredging and construction, and from there has diversified into a wide range of services, such as healthcare and catering, for clients in government and industry.
It sells services, including probation, cleaning and healthcare, and is involved in construction projects.
It is the largest provider of probation services in England and Wales, supervising about 40,000 "medium-low risk offenders" for the Ministry of Justice.
Its infrastructure projects include improving the M5's Junction 6 near Worcester, refurbishing the Rotherham Interchange bus station in Yorkshire, and upgrading sewers and water pipes for Northumbrian Water.
And at King George Hospital in east London, for instance, Interserve has a £35m contract for cleaning, security, meals, waste management and maintenance.
Both the rescue deal and the pre-pack administration are designed to keep those contracts going and jobs in place, at least in the short term.
BBC business editor Simon Jack
Interserve, one of the government's biggest providers of public services, may go into administration later.
The firm is holding a crucial shareholder vote to decide whether to accept a rescue plan which would see its lenders write off hundreds of millions of pounds in debt in exchange for new shares.
It employs 45,000 people in the UK and relies on contracts to serve schools, hospital and the army for 70% of its revenue.
The company is drowning in £650m of debt and its woes have invited comparisons with failed contractor Carillion which went bust just over a year ago.
However, the government - which put Interserve under intense supervision 18 months ago - insists that if the rescue deal is not approved and the company does go bust, there is a plan to bring the company out of administration over this weekend.
This arrangement will see the lenders take control of the company, essential services will not be interrupted, but current shareholders will see their shares rendered worthless.
That includes the company's biggest shareholder, US firm Coltrane Asset Management, which has opposed the deal but is thought to be interested in buying pieces of the company after administration.
Whatever happens on Friday, the financial disaster at Interserve is certain to revive the debate around the role of the private sector in providing public services.
What has the reaction been so far?
The firm's shares have plunged over the past year. Just over a year ago, they were worth 100p each. Currently they're trading at 9.6p each.
The RMT union said that events around Interserve suggested the current business model of using outside contractors for public services was "broken". The union said the Interserve contract to clean and service railway stations in the southern section should be taken over by Network Rail.
General Secretary of the RMT Union, Mick Cash, said bringing the contracts in-house would "avoid a repeat of the Carillion chaos."
"Once again we see the reality of bandit capitalism and its toxic impact on our public services. The time has come to end this obsession with the private sector speculators and return to the principles of public services run and owned by the public, free from this corrosive nonsense," he said.