The Vietnamese travel agency that organized an excursion during which 11 tourists and their guide died when their boat sank last week was unlicensed, an official said Wednesday.
The Hanoi-based firm, Nu Hoang, "did not have a license authorizing it to conduct international tourism," said Vu Xuan Thanh, chief inspector at the Ministry of Culture, Sport and Tourism.
The guide who died in the sinking had neither a work contract nor a ministry-issued guide's identity card, Thanh told AFP.
The ministry has fined the company and ordered it to immediately stop serving foreign tourists, Thanh said, without specifying the amount of the penalty. He did not know if police would also investigate the firm.
The captain and engineer of the boat have already been arrested on safety violation charges punishable by a jail sentence.
Most of the victims on the budget tour were foreign tourists in their 20s. They died when their boat "Dream Voyage" suddenly sank as they slept on Halong Bay, one of Vietnam's most popular attractions.
Nine tourists and six crew survived the accident, which a senior provincial official said was most likely caused by water leakage resulting from human error.
Nguyen Van Hien, director of the Nu Hoang travel firm, said he was busy and turned off his mobile phone when AFP reached him.
He told the tourism ministry that his firm had contracts with hotels in Hanoi's Old Quarter tourist hub to collect visitors wishing to visit Ha Long Bay, Thanh said. It had a separate contract with Truong Hai company, which operated the boat.
The incident, which an official has called the worst-ever tourist accident in Vietnam, has highlighted safety standards in the industry.
Police have confirmed the Truong Hai company was involved in another deadly accident in September 2009 when it operated under a different name.
The dead included visitors from Russia, the United States, Sweden, Britain, Japan, France and Switzerland, as well as a Vietnamese living in Australia.