The amendment, tabled by Ronny Tong Ka-wah of the Article 45 Concern Group, called for a review of the current duty on diesel as well as a further review before December next year. It was passed with the backing of 20 directly elected lawmakers, with five against, and 23 from the functional constituencies, with two against and one abstention.

Stanley Chiang Chi-wai, a spokesman for the Joint Committee of the Transport Trade on Monitoring Fuel Prices, says the group is considering staging a slow-drive protest on Tsing Yi Island on November 16 if the government fails to cut the duty on diesel.

While Ms Lau's original motion was supported by the Democratic Alliance for Betterment of Hong Kong and several pro-democracy unionist legislators during the debate, it did not win the backing of the Democratic Party and The Alliance. The price of diesel has risen more than 20 per cent this year, to $7.36 a litre. Ms Lau said the price in Hong Kong was among the highest in Asia, and compared with $3.35 a litre in Shenzhen and $4.30 in Singapore.

'The concession for diesel duty should not be seen as a subsidy or favour for transport operators. Other sectors of our economy will be affected if the transport industry suffers from a soaring diesel price,' Ms Lau said.

Frederick Fung Kin-kee, chairman of the Association for Democracy and People's Livelihood, said that after tax, the retail price of diesel in Hong Kong was much higher than other countries, comparing it with $4.1 a litre in Japan and $2.84 in the United States.

Secretary for Financial Services and the Treasury Frederick Ma Si-hang said there was no room for further cuts in diesel taxes, which were a crucial source of revenue.

He said diesel duty in Hong Kong was lower than in many countries, with duty imposed in Britain, Germany and Australia ranging from $2 to $7 a litre.

The government decided last month to extend the duty concession on ultra-low-sulfur diesel until December next year in an attempt to ease the burden of soaring oil prices on the transport industry.

It stands to lose $1.1 billion in revenue from the 12-month extension.

The duty, originally $2 a litre, is now $1.11, but transport operators say that it is not low enough.

Pro-democracy lawmakers, including those from the Democratic Party, and Albert Cheng King-hon, warned that the plight of transport operators would not be eased by a reduction of diesel duty if the monopoly in the local oil market was not addressed.

Mr Tong said it was more important to set up a fair-competition mechanism in the oil market to ensure any cut in diesel duty would benefit end-users.

He said he had urged the financial secretary to look at the problems of transport operators within the next three months.

Organisers expect about 1,000 drivers of trucks, minibuses and taxis to join the slow-drive protest on Tsing Yi Island if the government fails to cut the duty on diesel.