BT's deal to buy mobile network EE for £12.5bn has raised "significant" competition concerns, according to regulators.
The Competitions and Markets Authority (CMA) will address the concerns after fast-tracking the probe into the more detailed second phase following a request from BT.
"We have found that there is a real risk that the merger could reduce their incentives to supply these inputs and that this could have a detrimental impact on the retail mobile market," said the CMA's markets and mergers executive director, Andrea Coscelli.
"BT and EE have recognised that the issues in this case are complex and that the test for reference at phase one would be met. They therefore requested use of the fast track procedure and, after due consideration, we believe this to be appropriate," added Coscelli.
The deal, sealed in February, will combine BT’s more than 10m retail customers and EE’s 24.5m mobile subscribers and will be funded through a £1bn share issue and £2.4bn of new debt.
The CMA launched its probe of the merger in mid-May. Rivals in the mobile and telecoms space, such as Vodafone, Sky and Talk Talk have raised concerns over the former publicly-owned company's power in the market.
BT earlier today announced its plans for broadcasting Champions League football next season. Former Liverpool striker Steven Gerrard and BBC pundit Gary Lineker have been lined up as commentators.