The UK’s competition watchdog is studying the proposed union of online gambling giants Flutter Entertainment and The Stars Group (TSG).

On Wednesday, the UK’s Competition and Markets Authority (CMA) announced an inquiry into the proposed deal to combine the operations of Flutter and TSG. The merger, which was announced last October, would create a gambling behemoth with estimated annual revenue of nearly £4b and a valuation of around £10b.

Given that the companies’ combined operations would control an estimated 40% of the UK’s online sports betting activity and around one-quarter of the UK’s overall online gambling market, the CMA believes a closer inspection of the deal is warranted to ensure it won’t result in “a substantial lessening of competition within any market or markets in the United Kingdom for goods or services.”

The CMA informed both companies of its decision on Tuesday and is now soliciting public comments on the proposed merger until February 18. The CMA plans to issue a ‘phase 1 decision’ on its findings by March 31, long before the two companies expect their deal to close by the second or third quarter of 2020.