China's ministry of commerce has extended its antitrust review of Marriott International's takeover of hotel giant Starwood Hotels & Resorts Worldwide by up to 60 days.
The competition authority requested an additional review period, known as phase three, to investigate the merger, the companies said in a joint statement.
If the tie-up of the two hospitality giants goes ahead, it will create the world's largest hotel group, with a combined enterprise value of $36bn (£28bn) and more than 1.1m hotel rooms.
Marriott and Starwood said they "continue to believe that their planned merger transaction poses no anti-competitive issues in China".
Approval by China's ministry of commerce is the only remaining merger clearance required before the transation may close.
More than 40 other markets have granted the tie-up premerger clearance, including the European Union, Canada, the US, South Africa and Japan.
Shareholders at both companies approved Marriott's $12.4bn takeover of Starwood in April, following a bidding war between Marriott and Chinese insurance behemoth Anbang.
Marriott and Starwood had originally struck a $12.2bn deal last November, before Anbang waded in and outbid Marriott in March.
It then walked away from the deal at the last moment citing "market considerations", allowing the originally-intended tie-up to move ahead.