Opponents of the move called the plan "reckless" and an "offence to the rule of law".

The government on Monday said it would introduce new laws aimed at side-stepping a decision by the Court of Appeal in August that found the licence for the extension of the Springvale coal mine was invalid because its operations harmed the quality of Sydney's drinking water.

The Court of Appeal sent the matter back to the Land and Environment Court for the parties to reach a resolution to allow the mine near Lithgow to continue operating.

By deciding to introduce new laws to protect Springvale's operations - and those of EnergyAustralia's Mount Piper power station that receives all its coal from the mine - the government is aiming to pre-empt the result of the parties' discussions.

Energy Minister Don Harwin said in a statement the new laws would ensure the Springvale mine could continue to supply Mount Piper, which now generates about 11 per cent of the state's electricity. The laws would also include "significant protections for the environment".

"Springvale Mine is the sole current source of fuel for Mount Piper power station, and we are keen to avoid any disruption to its functions," Mr Harwin said.

"My top priority as energy minister is to ensure NSW households and business have an affordable, secure and reliable energy supply - this decision supports that."

Planning Minister Anthony Roberts said the laws would continue to ensure any projects within the Sydney water catchment maintained or improved water quality, the key issue that triggered the Court of Appeal's decision.

"We are committed to maintaining the highest water quality standards," he said.

"That's why the legislation will support the construction of a water treatment plant to eliminate saline discharges from the mine."

Mr Harwin told a media briefing that the mine will have a water treatment plant running by mid-2019, so "you'll have no more discharge from the power station or the mine into the upper Coxs valley".

"To do anything other than pass the legislation that we're introducing tomorrow, runs the risk of blackouts during this summer, and an immediate spike in prices," he said.

The new legislation will aim to change the Environmental Planning and Assessment (EP&A) Act to clarify that projects in the Sydney water catchment seeking to expand must maintain or improve water quality compared with their existing consent, and will specifically validate Springvale mine's State Significant Development consent, the statement said.

'Offence to the rule of law'

Sue Higginson, chief executive of the NSW Environmental Defender's Office, said the government's action was "not rational".

"No government should pass special laws unless there is an absolute case to do so and even then only as an absolute last resort," Ms Higginson said.

"Special laws to validate unlawful acts by the executive is an offence to the rule of law.

"The proper thing to do in this situation, as inconvenient as it may be for Centennial Coal [owner of the Springvale Mine] and all involved is to wait until all of the expert evidence has been presented and the [Land and Environment] Court has made its finding based on all of the evidence," she said.

There was no need for a hasty move since the nearby power station had stockpiled enough coal to operate through the coming summer, Ms Higginson said.

Georgina Woods, a spokeswoman for Lock The Gate, said the government should have let the Land and Environment Court do its job.

The mine had not been ordered to close by the court, and had been operating continually since the victory by environmental group 4Nature in the Court of Appeal.

"The Land and Environment Court has a job to do to honour the law that protects the pristine quality of our drinking water from coal mining and other development," Ms Woods said.

"Weakening the law for the convenience of a coal mining company that is polluting drinking water is a reckless and unnecessary reaction," she said.

"Protecting drinking water should be our highest priority."