She said there was concern that Hong Kongers were losing their inhibitions when they go out drinking.
“Sometimes when people drink more, there may be some intimate acts,” she told reporters.
Supermarkets and alcohol retailers are not covered by the rule.
Last week, a cluster of infections was found among patients who had been out in Lan Kwai Fong, the city’s most famous nightclub street.
Hong Kong’s tabloids ran lurid pieces saying one of the patients who went to bars in Lan Kwai Fong, a local, may have had one night stands.
The vast majority of the recent spike in infections have been from Hong Kong nationals returning to the city.
But there has also been some anger directed at the drinking habits of some Western white-collar workers as many of the city’s inhabitants isolate themselves.
Last week the Apple Daily newspaper carried a front-page photograph of a big group of foreigners drinking in the open while sitting shoulder-to-shoulder, sparking outrage on social media.
Chin Chun-wing, vice chairman of the Hong Kong Bar and Pub Association, said the government did not consult or notify the industry before announcing the measure.
Bar staff in Wanchai, a popular entertainment district, said they now feared losing their jobs.
“It’s a disaster for us, we are just casual working people,” Romano, a 30-year-old bar worker from the Philippines, told AFP.