The Competition and Markets Authority (CMA) has announced an investigation into a $40 billion takeover of UK computer chip designer Arm Holdings.
US graphics chip specialist Nvidia agreed the deal to buy the company from Japan's Softbank Group in September last year.
Britain's competition watchdog has been scrutinising the sale, with the two companies expecting some action.
The CMA has invited interested third parties to comment on the impact the merger could have on competition in the UK.
Its formal investigation will begin later this year.
Arm technology's designs underpin processors made by Apple, Samsung, Sony and Huawei.