Google has breached a European Union court ruling by sending unsolicited advertising emails directly to the inbox of Gmail users, Austrian advocacy group noyb.eu said on Wednesday in a complaint filed with France's data protection watchdog.

The Alphabet unit, whose revenues mainly come from online advertising, should ask Gmail users for their prior consent before sending them any direct marketing emails, noyb.eu said, citing a 2021 decision by the Court of Justice of the European Union (CJUE).

While Google's ad emails may look like normal ones, they include the word "Ad" in green letters on the left-hand side, below the subject of the email, noyb.eu said in its complaint. Also, they do not include a date, the advocacy group added.

"It's as if the postman was paid to remove the ads from your mailbox and put his own instead," said Romain Robert, programme director at noyb.eu, with reference to Gmail's anti-spam filters that put most unsolicited emails in a separate folder.

Google did not immediately respond to requests seeking comment. A spokesperson for the CNIL confirmed the authority had received the complaint and that it was being registered.

Vienna-based noyb.eu (None Of Your Business) chose CNIL, among other national data privacy watchdogs, because it's known for being one of the most vocal regulators within the EU, Robert said.

While any CNIL decision would be only applicable in France, it could compel Google to review its practices in the region.

Noyb.eu is an advocacy group founded by Austrian lawyer and privacy activist Max Schrems who won a high profile privacy case at Europe's top court in 2020.

The CNIL imposed a record fine of 150 million euros ($149 million) on Google earlier this year for making it difficult for internet users to refuse online trackers.

($1 = 1.0051 euros)