LONDON — After European policymakers adopted a sweeping data privacy law last year, the big question was how regulators would use their newfound authority against the most powerful technology companies.

In the first major example, the French data protection authority announced Monday that it had fined Google 50 million euros, or about $57 million, for not properly disclosing to users how data is collected across its services — including its search engine, Google Maps and YouTube — to present personalized advertisements.

The penalty is the largest to date under the European Union privacy law, known as the General Data Protection Regulation, which took effect in May, and shows that regulators are following through on a pledge to use the rules to push back against internet companies whose businesses depend on collecting data. Facebook is also a subject of several investigations by the data protection authorities in Europe.

The ruling signals a new phase in enforcing the European law, which the region’s lawmakers and privacy groups have cheered as a check against the growing power of technology companies, while for general consumers it has led mostly to a frustrating increase in the number of consent boxes to click. The fine against Google is just the fourth penalty against any company since the law took effect.