On Monday Doan’s family of nine visited Minh Phi restaurant for lunch.
After finishing they were given a check for VND2.3 million (US$91), and Doan, suspecting they had been overcharged, asked the restaurant to check it carefully.
They had been charged VND756,000 for 10 roasted mantis shrimp and VND200,000 for a bowl of clam soup, and she protested at their excessive prices.
She said in response some staff of the restaurant were "vicious and aggressive, threatened her family and chased them out of the restaurant."
Some of her family members used their phones to record the incident.
They quickly reported to the police
An initial investigation found the restaurant had failed to list prices as required by law.
Police are continuing the investigation.
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.