A spike in electricity demand in South Australia and NSW on Friday as temperatures soar over 40 degrees could lead to blackouts.
The warning from the Australian Energy Market Operator comes as senators prepare to quiz it and renewable energy agencies at a public hearing in Canberra.
The AEMO released a market notice on Thursday afternoon notifying electricity generators of a "forecast potential shortfall" in NSW on Friday from 5.30pm AEDT.
Prime Minister Malcolm Turnbull says Labor's "ideological" push for more renewable energy is leading to a less reliable supply of electricity, especially in South Australia.
But Labor says the rules behind the energy market bind the hands of the operator, making it harder to get extra power into the system precisely when it's needed and avoid local "load shedding".
Load shedding can sometimes be required when there is an imbalance between electricity demand and electricity supply.
When there is a shortfall in the electricity supply, there can be a need to reduce demand very quickly to an acceptable level, or risk the electricity network becoming unstable.
Federal energy minister Josh Frydenberg has asked AEMO for an urgent report into what happened in SA, after the regulator offered a different account of why the gas-fired power station at Pelican Point wasn't turned on to prevent a blackout on Wednesday.
But he's warming to the idea of coal-fired power being reopened to stabilise the system.
Alinta Energy closed the Northern Power coal-fired station in Port Augusta last May and it is already partially demolished.
Representatives from AEMO, the Australian Solar Council, CSIRO, Australian Renewable Energy Agency and the Australian Energy Regulator will give evidence at Friday's hearing of the inquiry into the resilience of electricity infrastructure.