Dozens of petitioners staged an overnight candle-light vigil to call for the introduction of legislation on a minimum wage in today's policy address by Chief Executive Donald Tsang Yam-kuen. Last night's event was organised by the People's Alliance for a Minimum Wage, which was formed by more than 30 groups, including the Confederation of Trade Unions and the Justice and Peace Commission of the Hong Kong Catholic diocese. In his annual policy speech, Mr Tsang is expected to offer a voluntary minimum-wage charter to protect low-paid workers in the cleaning and security industries first. He is expected to promise to review the need for legislation in two to three years, sources familiar with the issue have said. Another main topic of the address, entitled 'Proactive, Pragmatic and Always People First', is improving Hong Kong's air quality. Mr Tsang is expected to announce a cash subsidy scheme or a first-registration-tax waiver to help owners of older trucks that don't meet the most basic emission standards buy models that pollute less. He is likely to respond to calls to promote environment-friendly cars, such as those using hybrid engines, but a city-wide ban on idling engines is unlikely, according to sources close to the government.