Renault SA shares plunged the most in 17 years after a union said French fraud investigators seized computers from the automaker, apparently as part of a probe into emissions testing.

Agents from the Economy Ministry’s fraud office visited some Renault sites that have to do with standards testing and engine certification, Florent Grimaldi, an official with the CGT union in Lardy, France, said by telephone Thursday, confirming a report earlier by Agence France-Presse. That left the impression that the probe is related to emissions standards in the wake of the Volkswagen AG scandal, he said.