Power-company labour unions say their members' jobs will be under threat if Hong Kong imports more electricity from the mainland to replace local coal-fired generation.
And even if the city were to adopt an alternative option of burning more natural gas, there would still be some impact on employment, the unions say.
Sze Sang-tai, chairman of the CLP Power Chinese Employees Union, estimates that up to 4,000 workers whose jobs are directly and indirectly related to the operation of coal units and the associated supply chain will be affected if coal burning is reduced significantly.
"Up to 4,000 families' livelihoods will be under threat and pressure.
"No matter whether they are workers, contractors or suppliers, their jobs will face uncertainty," Sze said.
He added that while the local-generation option was a lesser evil than the import option, greater use of gas could still lead to a loss of jobs.
Coal burning requires up to four times as many workers as gas burning.
"The loss of jobs will not be confined to those involved in operation, but also those who maintain the units, and who transport coal and the coal ash," he said.
About 60 per cent of the city's power is currently generated from coal burning, and most of the generation units at both CLP Power and Hongkong Electric are driven by coal.
CLP Power has 3,700 employees and Hongkong Electric about 2,000.
Sze questioned whether a government consultation on the two options placed enough emphasis on jobs.
"Why do we have to choose from either one of the two? Do we have a third option that pays more attention to the workers' needs?" he asked.
Sze said the power unions were working with the Federation of Trade Unions to put together a response to the government consultation.
Dr Chan Fuk-cheung, a veteran power system engineer who previously worked for CLP Power, said the workers could be worrying unduly about imports.
"Automation is the workers' biggest threat, rather than power imports. In fact, CLP Power cut its manpower from a peak of 6,000 to about 4,000 in the late '90s," he said.
He believed the company would try to keep experienced staff and retrain them for other posts.