General Motors' stock price is tumbling after reports that the carmaker is accused of putting defeat devices in its trucks to beat emissions tests, becoming the sixth carmaker accused of diesel cheating since 2015, when Volkswagen AG admitted to installing software to bypass pollution rules.

Bloomberg reports that People who own or lease more than 705,000 GM Duramax diesel trucks filed a class-action lawsuit Thursday, claiming GM installed multiple such devices in two models of heavy-duty trucks from 2011 to 2016.

The 190-page complaint is littered with more than 80 references to VW, and asserts that the environmental damage caused by each truck could surpass that of the German automaker’s vehicles.

And the result is GM down 4%...