Greenpeace is calling for electricity bills to be frozen for small businesses and residential users who consume less energy.
The demand came after it studied public information on CLP Power, which showed small businesses had lost out on tariff cuts in the last nine years.
They found small businesses consuming not more than 1,500 kilowatt hours per month had seen their basic tariff reduced by about 6.9 per cent since 2004.
But bulk users benefited from a cut of up to 12.9 per cent.
Greenpeace's Prentice Koo Wai-muk said: "Given their lower cut, there should be a tariff freeze for small businesses in the coming year." Koo said residential users consuming less energy should also have their tariffs frozen next year.
In a reply, CLP denied Greenpeace's allegations and said it had offered incentives to encourage commercial users to consume less power in peak periods.
CLP also said it had a GreenPlus scheme to help small and medium-sized enterprises devise measures to use energy more efficiently by offering such services as consumption analysis and check-ups, or advice on energy efficient building design.
At the Harbour City shopping arcade yesterday in Tsim Sha Tsui, four Greenpeace activists covered the outdoor television screen above the main entrance with a banner. It read: "Shopping malls gets 40 per cent discount for electricity bills, while ordinary citizens need to pay more."
The group's call comes as the government is scrutinising the tariff adjustment proposals of CLP Power and Hongkong Electric for next year.
Power tariffs consist of two parts. The basic tariff reflects capital investment on power generation and distribution, and then there are the fuel costs, which are passed on directly to consumers.
CLP increased tariffs by 4.9 per cent last year - a significantly lower increase than the 9.2 per cent rise initially proposed, which led to a public outcry and was described by the government as an excessive increase.
Earlier this year, CLP Power chairman Michael Kadoorie warned of a 40 per cent price rise by the end of 2015. He said the cost of new gas, under a contract agreed 20 years ago, would be three times the existing supply.
CLP Power's average charge per kilowatt hour is 98.7 HK cents, which it says remains one of the lowest in the region.
Greenpeace also queried CLP Power's importing of more expensive nuclear power from the mainland, while it exported cheap electricity over the border.
A CLP spokeswoman said last night there was no relationship between nuclear energy imports and electricity exports.