The US tech giants have been hit with fines totalling 210 million euros ($125 million), after the CNIL - the data privacy watchdog - determined that both firms were making it tough for internet users to refuse the online trackers.
Karin Kiefer, the CNIL's head of data protection and sanctions, told the BBC: "When you accept cookies, it's done in just one click.
"Rejecting cookies should be as easy as accepting them."
In response to the ruling, Google said: "People trust us to respect their right to privacy and keep them safe.
"We understand our responsibility to protect that trust and are committing to further changes and active work with the CNIL in [the] light of this decision."
Facebook, on the other hand, confirmed that it was still reviewing the ruling and is trying to plot its best route forwards.
The tech giant said after the fine was confirmed: "Our cookie consent controls provide people with greater control over their data, including a new settings menu on Facebook and Instagram, where people can revisit and manage their decisions at any time, and we continue to develop and improve these controls."