Bar managers and store owners face large-scale compensation claims if their customers ogle their barmaids, waitresses or check-out staff.
New sex discrimination laws also mean that landlords who allow loud sexist jokes or banter among drinkers could be taken before a tribunal.
The regulations say that bosses are responsible for protecting their staff from sexual harassment by customers - and that those who fail to do so can face unlimited compensation claims.
....Restaurant managers or hoteliers risk action if staff object to backchat from diners or guests asking for a date.
....The regulations were pushed through by Women and Equalities Minister Harriet Harman, who has powers under European legislation to amend discrimination law.
....Stuart Chamberlain, an employment law specialist at Consult GEE, said: "Employers may feel uncomfortable about confronting clients but they need to be aware that failing to take action could result in a claim for compensation, including for injury to feelings.
....The burden of proof will lie with employers. There will be no need for workers to show their employer allowed harassment to happen - instead, managers must demonstrate that they were not at fault.