China’s Ministry of Commerce (MOFCOM) review is the only remaining merger clearance for the deal, which is expected to create the largest hotel group in the world with a combined enterprise value of $36 billion and 1.1 million hotel rooms.

Hilton Worldwide (HLT), which would be No.2 behind the combined group, has 775,000 rooms.

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Marriott and Starwood did not say why MOFCOM needed more time and said their planned merger did not create any anti-competitive issues in China.

The merged group would become the largest hotel operator in China with a 4.1% market share, followed by Homeinns Hotel & Management at 4% and China Lodging Group at 3.9%, data from research firm Euromonitor International shows.

Marriott’s deal to buy Starwood, the operator of Sheraton and Westin hotels, has been cleared by antitrust authorities in more than 40 countries and territories including the United States, the European Union and Canada.

The shareholders of both companies approved the deal in April.

MOFCOM has developed a reputation as a tough deals regulator, but it has only blocked two transactions since China’s antimonopoly law came into force in 2008, compared with 1,447 unconditional clearances, according to data compiled by law firm Norton Rose Fulbright.

The regulator generally prefers to impose remedies such as asset divestments on transactions it believes could harm competition, taking this approach in 26 cases, the Norton Rose Fulbright research shows.

Last month, MOFCOM approved AB InBev’s $100 billion-plus takeover of rival brewer SABMiller subject to SABMiller divesting some Chinese assets. MOFCOM also extended InBev’s review to phase-three, but did not make full use of the extra time.

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A Chinese company, Anbang Insurance, abandoned its pursuit of Starwood in April after a bidding war that resulted in Marriott increasing its cash-and-stock bid by $1 billion. The deal is currently valued at about $13.4 billion.

While Anbang had offered $14 billion in cash, an acquisition by the Chinese firm probably would have faced scrutiny by the Committee on Foreign Investment in the United States on national security grounds.

Once notorious for its lengthy review process, MOFCOM has significantly sped-up approvals over the past 18 months following the introduction of a simple case procedure that takes about 29 days. Still, complex transactions can spend months in limbo.

Deals filed via the normal procedure undergo a 30-day phase-one review, which can be extended by 90 days for phase two and by a further 60 days for the final third phase. Including pre-filing consultations with MOFCOM, a deal that goes to phase three could take nine months to clear.

Unlike the European Union, MOFCOM does not operate a specific threshold for moving beyond phase one, and may do so for administrative reasons or because the watchdog is short of resources, lawyers said.