Heineken and investment partner Patron Capital struck a 403 million pound deal December to buy and break up Punch Taverns, paving the way for Heineken to become Britain's third-biggest pubs group.
Britain's Competition and Markets Authority (CMA) said it has looked at areas where pubs operated by Heineken and Punch currently compete and identified 33 locations where their pubs would not face sufficient competition after the merger, which could lead to price rises and poorer customer service.
CMA said Heineken has until June 20 to offer proposals to address the concerns or face an in-depth investigation into the merger.
Punch, in a separate statement, said that both companies are now putting together a plan to the regulator to address the points raised and are confident that the deal would be approved without an investigation.
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