The European Commission said Tuesday that it has opened an in-depth investigation into Alphabet Inc.'s /zigman2/quotes/205453964/composite GOOG +1.35% /zigman2/quotes/202490156/composite GOOGL +1.36% proposed acquisition of Fitbit. "The Commission is concerned that the proposed transaction would further entrench Google's market position in the online advertising markets by increasing the already vast amount of data that Google could use for personalisation of the ads it serves and displays," the European Commission said in a release. Executive Vice-President Margrethe Vestager commented in the release that Google's acquisition of Fitbit could give the ad giant "key insights about the life and the health situation of the users of these devices," so this investigation "aims to ensure that control by Google over data collected through wearable devices as a result of the transaction does not distort competition." A Reuters report from mid-July said that Google had offered not to use Fitbit health data for the purposes of ad targeting given European Commission concerns. The commission has 90 working days, or until Dec. 9, to reach a decision. Fitbit shares are down 0.4% in Tuesday trading, while Alphabet shares are up 0.3%. Fitbit shares have lost 1.8% so far this year as Alphabet's stock has gained 11% and as the S&P 500 /zigman2/quotes/210599714/realtime SPX +1.61% has risen 2%.