California Air Resources Board

The U.S. Justice Department plans to file a civil lawsuit against Fiat Chrysler Automobiles NV over excess diesel emissions as early as this week if no agreement is reached with the Italian-American automaker, two sources briefed on the matter said on Wednesday.

Shares in German auto giant Volkswagen fell more than 13 percent on the Frankfurt stock exchange on Sept. 21 after it emerged some of its diesel cars in the United States had been fitted with software that gave false emissions data.

In the first few minutes of trading, VW shares fell by as much as 13.23 percent to 140 euros in a slightly lower market.