LONDON (AP) — The U.K. competition watchdog is investigating Amazon’s purchase of a significant stake in food delivery service Deliveroo.

The Competition and Markets Authority decision Friday will put any merger plans on hold. The authority says it has “reasonable grounds for suspecting” that the deal could “result in Amazon and Deliveroo ceasing to be distinct.”

Deliveroo says the investment will “enable Deliveroo to expand, innovate and, we believe, will enhance competition.” Amazon says the expansion will benefit consumers by increasing choice and by “creating new jobs as more restaurants gain access to the service.”

The exact amount spent on the stake is unclear, but Deliveroo’s last fundraising round brought in 450 million pounds ($564 million.)

The CMA could block any deal, as it did recently by halting the attempted merger of Sainsbury’s and Asda.