It’s a matter of licensing.

According to the TokyoReporter: “Hidetoshi Kawada, 38, of no fixed address, was cited by prefectural police on April 20 for staffing club B with ladies positioned behind a counter, lacking bras and attired in loose-fitting shirts, high-cut shorts, and pantyhose — a violation of the Law Regulating Adult Entertainment Businesses given the club’s licensing as an eating and drinking venue and not a locale of adult entertainment.”

This will become an increasingly frequent issue as the number of ‘girls bars’ increases. Not uncommon in other Asian countries, these eating establishments are staffed entirely by young women. These are usually partnered with more adult entertainment establishments. The police reported that the bar was open since October and earned an average of 3,500,000 – 4,500,000 yen per month.

source: Sankei News