BT’s £12.5 billion acquisition of EE could harm mobile competition in the UK market, according to Which? magazine.
The merge of O2 and Three-owner Hutchison Whampoa could also put the competition in the UK’s mobile industry at risk.
Richard Lloyd, executive director of Which?, believes that the deal could see prices increase with customer’s receiving a poorer service.
Lloyd said: "This deal would signal more significant change to the UK telecoms market, with O2 and Three also expected to merge.
“Fewer players in any essential market is rarely good for consumers.”
The deal combines BT’s 10 million retail customers and EE’s 24.5 million mobile subscribers, which could result in less competition within the UK’s mobile industry.
"The competition authorities must now look at both the proposed mergers and the market in the round to make sure that consumers are protected from unfair price increases or poorer service as a result of less competition," added Lloyd.
Following the acquisition of EE, Deutsche Telekom and Orange will now hold stakes of 12 per cent and four per cent in BT respectively.