Objecting parents say the measure is unnecessary and will add to the costs of sending their children to the school, where total annual fees range up to HK$210,900.

But the school's communications and public relations manager, Arlene Vermylen, said HKIS believes mandatory busing is the best option to ease the rush-hour gridlock around the school.

The school has proposed constructing a multimillion-dollar, "state-of-the-art" facility for its lower primary division on the site of the existing campus. It has faced stiff opposition from local residents, who worry that the new building could block views from their homes and contribute to traffic congestion in the area.

"As we worked to move the lower primary redevelopment project forward, it became clear that the heavy traffic at our Repulse Bay campus had been an ongoing issue for many years," Vermylen said. "The situation presents environmental and safety concerns as well as difficulty for our neighbours."

Some parents see it differently. "The road at the school is a public road that doesn't exclusively belong to the school. I don't see how it is legal to enforce how our kids commute once leaving the school's premises," one father said.

"We have a chauffeur that has been with us ever since our kids were born. Now we may have to terminate his employment due to this policy," said the father, who wished to remain anonymous due to what he described as "threatening tactics" by the school.

A statement on the HKIS website says if parents do not comply with the rule, their children's enrolment may be "jeopardised".

"Mandatory busing will force families to spend at least an additional HK$8,000 to HK$15,000 per child per family, when they previously were able economically to take public transport, walk or drive by private car," said another parent in an e-mail addressed to Southern District councillor Fergus Fung Se-goun, seen by the .

"Traffic problems have been our main concern. We have seen a phenomenon where the roads become blocked and local residents can't even leave their buildings," Fung said.

According to a statement on the school website, the plan is part of the redevelopment of the campus now under way, as well as "ongoing efforts to be a good neighbour".

Jing Wu, mother of a student soon to enrol at the school, supported the idea. "For me, it's great. I've just arrived [in Hong Kong] and I don't have to waste time worrying about transportation," Wu said. "But, I understand the problems of other parents. If they are living in Central or Admiralty, it will mean their children have to get up earlier."