Google is breaking EU law by sending users of its email service Gmail direct advertising messages, activists said in a complaint sent to French regulators on Wednesday.

It is the latest in a long line of complaints filed by the activist group NOYB (None of Your Business), which has fought the tech giant for years on data privacy.

The French data regulator CNIL has been among the most active in Europe, doling out huge fines against Google and Facebook in particular.

The activist group provided screenshots to CNIL that showed marketing messages at the top of a user’s inbox.

The messages were marked with a green box and the word "annonce", French for advert.

The group said under EU law, that kind of marketing was allowed only if users had consented.

"Spam is a commercial email sent without consent. And it is illegal," said NOYB lawyer Romain Robert in a statement.

"Spam does not become legal just because it is generated by the email provider."

CNIL confirmed to AFP it had received the complaint.

Google told AFP it had no comment as yet.

Google and Facebook’s parent company Meta are at the centre of a long-running battle over their data-collection practices in Europe.

The French regulator fined Google 150 million euros ($150 million) and Meta 60 million euros last December over their failure to provide users with an easy opt-out for cookies, files that track users around the web.

The two firms also face scrutiny over their practice of sending the personal data of EU residents to servers in the United States. 

NOYB has filed dozens of cases with regulators across the bloc arguing that the practice is illegal.