Criminal probe opened into Volkswagen, stock plunges Investors are grappling with the automaker's decision to stop selling diesel cars in the U.S. until it can fix the vehicles.

Show Caption Hide Caption Bloomberg: Justice Dept. is conducting VW emissions investigation Sept. 21 -- The U.S. Justice Department is conducting a criminal investigation of Volkswagen's admission to cheating on federal air pollution tests, according to two U.S. officials familiar with the inquiry.

The Justice Department has opened a criminal probe into Volkswagen's admission that it rigged 482,000 diesel cars in the U.S. to beat emissions tests as investors hammered the automaker's stock Monday, sending shares plunging 18.6%.

Disclosure of the criminal probe, confirmed by a U.S. official who is not authorized to comment publicly, comes after VW's CEO, Martin Winterkorn, offered an apology Sunday for cheating on emissions tests. VW has halted sales of the affected models.

As if VW wasn't having enough trouble in the fallout, the House Energy Committee's oversight subcommittee announced it plans to hold a hearing on the Volkswagen case in coming weeks.

Shares of the German automaker — the world's largest vehicle manufacturer through the first six months of 2015 — closed at 132.50 Euros, or $149.32, down 30.20 Euros, or $34.11, in trading in Europe.

Investors are absorbing the blow of the automaker's decision to halt sales of new and used four-cylinder diesel cars in the U.S. until it can remove software that fooled regulators into believing that its smaller "clean diesel" cars were compliant with emissions standards.

Fitch Ratings said Monday that the scandal could put pressure on the automaker's credit rating, but it noted that Volkswagen's financial performance remains "extremely robust" globally.

"Nonetheless, the consequences of this crisis for the group's brand image and reputation with regulators and consumers worldwide is difficult to assess," Fitch said.

The Environmental Protection Agency and California state regulators on Friday accused Volkswagen of installing a "defeat device" to evade emissions requirements.

Justice Department spokesman Wyn Hornbuckle declined comment.

The criminal probe, first reported by Bloomberg News, is the latest in a series of probes involving alleged wrongdoing by automakers. General Motors just agreed to pay $900 million to settle a criminal probe into faulty ignition switches. It is paying compensation for 124 accident-related deaths.

Toyota shelled out $1.2 billion in 2014 after an investigation into its handling of unintended-acceleration cases.

The VW case stands apart, however, because unlike the GM and Toyota cases where bungling or footdragging appeared to be at the heart of the allegations, this one involves an admission of outright deception.

Diesels represent about 20% of the automaker's sales in the U.S., according to AutoPacific. The cars affected by the situation are the four-cylinder diesel versions of the 2009 to 2015 Jetta, Beetle, Golf, the 2014 and 2015 Passat and the 2009 to 2015 Audi A3.

The diesel cars emit nitrogen oxides, which can exacerbate respiratory conditions such as asthma, at up to 40 times the acceptable level.

The EPA has the authority to fine Volkswagen up to $37,500 per vehicle, which could technically add up to a fine of some $18 billion, though analysts don't expect the agency to levy a fine of that magnitude.

The automaker could also face accusations of false marketing and consumer lawsuits over its promotion of the vehicles under the "Clean Diesel" moniker, in addition to the likely cost of a large recall.

Fitch said class-action lawsuits could lead to additional costs for Volkswagen over the next two years.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.