It’s not just the Environmental Protection Agency Volkswagen has to worry about. Now, the German car manufacturer’s stock price is taking a major hit.

Last week, the EPA ordered Volkswagen to recall about half a million vehicles, alleging that the company had used software in diesel-powered vehicles to cheat on U.S. emissions tests. On Sunday, the company announced it would halt U.S. sales of certain diesel-powered cars that the EPA says use the software, including 2015 and 2016 Volkswagen and Audi models that had been advertised to customers as “clean diesel.” Now, the market is responding accordingly, with the company’s stock price falling nearly 20 percent since Friday.

The drop is a clear reaction to the fact that Volkswagen will now miss out on a key market in the U.S. and may well be slapped $18 billion in fines, according to Reuters.

Volkswagen CEO, Martin Winterkorn, for his part, has issued an apology, saying in a statement, “I personally am deeply sorry that we have broken the trust of our customers and the public.”