According to local authorities, Minh Phi Restaurant in Ha Khau Ward failed to clearly list prices as regulated, causing misunderstanding among customers, and indulged in "unethical behavior."
Its owner was also forced to call up the tourists and apologize.
Last week the nine tourists went to the restaurant for lunch.
After finishing their meal, they were given a check for VND2.3 million. They suspected they had been overcharged and asked the restaurant to check it carefully.
In response, some of the staff became "vicious and aggressive, threatened their family and chased them out of the restaurant."
The tourists used their phones to record the incident and reported it to police and local authorities who dispatched an inspection team to investigate.
According to the city people's committee, the number of visitors to Ha Long has increased recently to 40,000-60,000 a day and over 70,000 during weekends.
Authorities have pledged to crack down on tourist scams to protect its tourism reputation.