After being given the green light, the new company will have a combined customer base of around 35 million mobile, broadband and TV customers.
Despite the criticisms, John Wotton, who chaired the CMA inquiry into the deal, said the evidence "does not show that this merger is likely to cause significant harm to competition or the interests of consumers".
Broadband and mobile provider TalkTalk is one such industry player that is not happy with the new deal.
"We are disappointed, although not surprised, that the CMA has waived through the BT/EE merger, even though the new entity will be even more dominant than it was before privatisation 30 years ago," it said.
Which? executive director, Richard Lloyd, added: "Fewer players in a market is rarely a good thing, but now this deal has been approved both companies must urgently address their abysmal customer service record.
"The regulator will...