Google faces a lengthy European Union probe into its $2.1 billion takeover of Fitbit Inc amid concerns about how health data could strengthen the search giant’s power in online advertising.

The EU will investigate how information from Fitbit’s fitness trackers will increase Google’s “data advantage” in online advertising that rivals would struggle to match, the European Commission said in a statement on Tuesday. Officials set an initial December 9 deadline to approve or veto the deal.

Regulators are increasingly scrutinising Silicon Valley takeovers, aiming to prevent the already powerful firms from conquering innovative new markets where data is often the most prized asset. Privacy and consumer advocates have been calling on the EU to examine how the deal could allow the Alphabet Inc. unit to expand into healthcare.