LONDON (AP) — European Union regulators say they're opening an in-depth investigation into U.S. tech giant Google's plan to buy fitness tracking device maker Fitbit

The EU's executive commission said Tuesday it's concerned the deal would entrench Google's position in the online ad market by "increasing the already vast amount of data" that the company could use to personalize ads.

EU competition commissioner Margrethe Vestager said the "investigation aims to ensure that control by Google over data collected through wearable devices as a result of the transaction does not distort competition."

Google agreed to buy Fitbit in November for $2.1 billion. Privacy and consumer groups have called on authorities to block the deal, citing privacy and antitrust concerns.

Google did not respond immediately to a request for comment Tuesday.

The investigation underscores the leading role European Union authorities have taken in global efforts to regulate the big technology companies.

Vestager has been at forefront of the movement to rein in the likes of Google and its Silicon Valley rivals. During her first five-year term as competition commissioner, she slapped Google with nearly $10 billion in penalties for multiple antitrust cases involving its Android operating system, advertising business and shopping service.

The EU said that it was concerned the deal would expand Google's "data advantage," and therefore raise barriers for rivals to match Google's online advertising services.