Amazon.com Inc.’s $1.65 billion bid to buy vacuum cleaner maker iRobot Corp. faces an in-depth European Union investigation amid concerns the takeover could hurt competition.

The European Commission, the EU’s merger watchdog, set a deadline of Nov. 15 to vet the potential impact of deal, which has sparked a backlash from privacy activists.

Aside from thwarting rival robot vacuum cleaners, Amazon’s access to iRobot’s users’ data could give it “an important advantage in the market for online marketplace services to third-party sellers,” the EU regulator said. “Thus, the transaction may raise barriers to entry and expansion for Amazon’s competitors to the detriment of consumers.”

The decision puts the commission at odds with Britain’s Competition and Markets Authority, which has given the deal the green light after concluding that iRobot has a relatively modest market power.

So-called phase 2 probes add about 90 working days to deal reviews. Regulators typically demand remedies to solve competition concerns but sometimes also decide to give their unconditional approval if initial concerns are shown to be unfounded.