Fears of another WorldCom have grown as US telco Qwest admitted it is under criminal investigation by the US Attorney's office.
In a brief announcement, the Colorado-based firm said it was notified by the Attorney's Office on Tuesday afternoon and would fully cooperate with the investigation.
But the exact nature of the investigation has not been disclosed.
The news sent its shares down to $1.67 on the New York Stock Exchange, losing 35.6 per cent of its value.
This follows on from a report last Friday in the Wall Street Journal that the US Department of Justice had launched a criminal investigation into the troubled telco, citing people with knowledge of the situation.
The Securities and Exchange Commission is also probing the firm's accounts.
Qwest has been under considerable pressure for some time now as it struggles under a $26bn (£18bn) mountain of debt. Credit rating agencies have marked its debt down to 'junk' status.
Last June, Qwest ditched its chairman and chief executive, Joseph Nacchio, in a bid to prop up its share price and allay investor fears.
The disclosure is just the latest in a series of high-profile companies to come under examination from US government agencies.
Cotton seedling freezes to death as Chang'e-4 shuts down for the Moon's 14-day lunar night
Fortnite easily out-earns PUBG, Assassin's Creed Odyssey and Red Dead Redemption 2 in 2018
Meteor showers as a service will be visible for about 100 kilometres in all directions
Saturn's rings only formed in the past 100 million years, suggests analysis of Cassini space probe data
New findings contradict conventional belief that Saturn's rings were formed along with the planet about 4.5 billion years ago