UK regulators will push to get involved in reviewing the proposed merger between Orange and T-Mobile that will create the UK's largest mobile operator.
Orange owner France Telecom and T-Mobile owner Deutsche Telekom have been lobbying for the merger to be reviewed only by European authorities in the hope of a quicker and easier approval.
They are concerned that the longer it takes for the deal to be approved, the greater the risk will be of losing customers to rivals.
But UK consumer groups have been calling for UK authorities to review the merger because of concerns about how reduced competition will affect the local market.
The merger will reduce the number of UK mobile network operators from five to four.
The UK Office of Fair Trading (OFT) is expected to ask the European Commission to scrutinise the merger, according to the Financial Times, which cites "people familiar with the situation".
If the EC agrees, the OFT inquiry is likely to be followed by an investigation by UK competition authorities, which could be more rigorous than any European review, competition lawyers said.
Mobile operators O2 and 3 have also called for UK authorities to review the merger because of concerns that the new company will hold most of the radio spectrum at the 1,800MHz bandwidth.
Equal access to this bandwidth has been hotly debated in the past year because it can be used for next-generation wireless technology that will enable faster web surfing on mobile phones.
By combining the spectrum shares of Orange and T-Mobile, the merger will undo the sharing agreement brokered by the government in recent months to end a long-running dispute.