LONDON (AP) — British antitrust regulators are opening an investigation into Microsoft's $16 billion acquisition of speech recognition company Nuance in the latest sign they're tightening scrutiny of big technology deals.

The Competition and Markets Authority said in a brief statement Monday that it's looking into the purchase because of concerns that it could result in a "substantial lessening of competition" in the U.K. market.

Redmond, Washington-based Microsoft Corp. said in April that it was buying Nuance Communications Inc., a pioneer in voice-based artificial intelligence technology. Nuance was instrumental in helping power Apple's digital assistant Siri but later shifted to focus on health care with widely used medical dictation and transcription tools.

The transaction, which was expected to close this year, would be Microsoft's second-largest deal, following the software giant's $26 billion purchase of LinkedIn in 2016. Burlington, Massachusetts-based Nuance has about 7,100 employees, more than half of whom are outside the U.S.

British regulators have stepped up scrutiny of tech-related acquisitions. Last month, the competition authority ordered Facebook to undo its purchase of Giphy and sell off the GIF-sharing platform because it found the deal stifles competition for animated images and hurts social media users and advertisers.