Google has been fined 100 million euros (£91m) in France for breaking the country's rules on online advertising trackers known as cookies.
It is the largest fine ever issued by the French data privacy watchdog CNIL.
US retail giant Amazon was also fined 35 million euros for breaking the rules.
CNIL said Google and Amazon's French websites had not sought visitors' consent before advertising cookies were saved on their computers.
Google and Amazon also failed to provide clear information about how the online trackers would be used, and how visitors to the French websites could refuse the cookies, the regulator said.
It has given the tech giants three months to change the information banners displayed on their websites.
If they do not comply, they will be fined a further 100,000 euros per day until the changes are made.
In a statement published by Reuters, Google said: "We stand by our record of providing upfront information and clear controls, strong internal data governance, secure infrastructure, and above all, helpful products.
"Today's decision under French ePrivacy laws overlooks these efforts and doesn't account for the fact that French rules and regulatory guidance are uncertain and constantly evolving."
Amazon said it disagreed with the CNIL decision,
"We continuously update our privacy practices to ensure that we meet the evolving needs and expectations of customers and regulators and fully comply with all applicable laws in every country in which we operate," it said in a statement.
In a separate case, Google is being probed by a UK regulator over its plans to change the way the Chrome browser handles cookies.
Google wants to stop advertisers using cookies to track users as they move around the web from one site to another when using Chrome, in a bid to improve privacy.
It plans to introduce an alternative system know as the Privacy Sandbox that will only provide anonymised feedback.
A group of about a dozen small tech companies and publishers has lodged a complaint with the Competition and Markets Authority (CMA) claiming this would damage their businesses.
The CMA is expected to announce whether it will intervene over the coming weeks.