The U.K.'s competition regulator said it would investigate Amazon's (AMZN) - Get Report recent investment in food delivery start-up Deliveroo in another sign of growing scrutiny of the dominance of giant U.S. tech companies. 

Britain's Competition and Markets Authority said on Friday it had "reasonable grounds" to suspect that Amazon and Deliveroo would "cease to be distinct" and essentially merge, following Amazon's leading of a $575-million funding round in Deliveroo in May. The six-year-old Deliveroo is one of the most popular food delivery companies in Europe. Amazon shut down its own restaurant delivery service in the U.K. last December, and shuttered its one in America in June. 

Amazon shares were down 0.5% to $1,929.29 on Friday morning, compared to a decline of 0.6% for the Nasdaq.

A spokesman for Amazon told the New York Times on Friday that "we believe this minority investment will enable Deliveroo to expand its services, benefiting consumers through increased choice and creating new jobs as more restaurants gain access to the service."

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