The probe is said to target the sites' engine control units
French anti-fraud police have raided several production sites belonging to car manufacturer Renault, according to media reports.
Local unions have reported that several Renault sites were visited by anti-fraud detectives last week, but both Renault and the French finance ministry have declined to comment.
According to the CGT Renault union, the probe targeted the sites' engine control units which they say would suggest the raids were linked to the Volkswagen emissions scandal.
However there has been no official confirmation of this so far.
The union also claims that the police seized the computers of several company directors.
Renault stocks have fallen 20% at the news.