Former Worldcom boss Bernard Ebbers is due to be sentenced later on Wednesday in New York for his part in the scandal which brought down the firm.
Prosecutors have called for Mr Ebbers to be given a life sentence
Mr Ebbers was found guilty of fraud and conspiracy in March, following revelations of an $11bn (£6.2bn) accounting fraud at Worldcom in 2002.
The 63-year-old, who was also found guilty of seven counts of filing false documents, could face life in jail.
Worldcom's collapse was the biggest bankruptcy in US corporate history.
Some 20,000 workers lost their jobs, while shareholders lost about $180bn, when the company filed for bankruptcy protection.
Worldcom emerged from bankruptcy last year and is now known as MCI.
'Enormity of crimes'
Prosecutors have asked US District Judge Barbara Jones to follow a probation report suggesting that Mr Ebbers should receive a life sentence for his part in the scandal.
Biggest US bankruptcy
Founded in 1983, Worldcom was the second biggest long distance phone firm in the US with 20 million customers.
It ran into numerous difficulties during the technology boom and got into debts of $41bn.
The accounting irregularities were revealed in June 2002.
Worldcom originally put a value of $4bn on the financial black hole. That has been slowly rising, first to $7bn, then $9bn and is now thought to total $11bn.
Total losses to shareholders since Worldcom's collapse are $180bn.
"The enormity of the crimes that Ebbers committed cannot be overstated. The fraud at Worldcom was the largest securities fraud in history," the prosecution wrote in papers presented to the court last month.
Mr Ebbers has asked for a sentence "substantially below" life in prison, citing the poor state of his health and his previous work for charity.
The sentence will come a day after the judge rejected a bid by Mr Ebbers for a new trial.
The former basketball coach and milkman argued that the court should have granted immunity to three witnesses he believed could have helped clear his name.
His lawyers also argued that jurors were given improper instructions when they considered the case.
Mr Ebbers resigned as chief executive of Worldcom in 2002, shortly before the fraud scandal at the firm become known.
He has always contended that the fraud was the work of his former finance chief Scott Sullivan, and that he knew too little about what was going on to be culpable.
Mr Sullivan, who pleaded guilty to the charges levelled against him, claimed his actions were directed by his boss.
Five senior Worldcom officials, who all pleaded guilty in the fraud and co-operated with the prosecution against Mr Ebbers, will be sentenced later this year.
Separately, a judge on Monday backed a multi-million dollar settlement under which Mr Ebbers must surrender most of his personal assets, including $5m in cash, to resolve a shareholder lawsuit.
The settlement will leave Mr Ebbers' wife with about $50,000 of her husband's fortune, and a modest home in Jackson, Mississippi.
However, the deal will see Mr Ebbers lose major assets including a mansion, a golf course, a lumber mill, and a grain elevator company.