The attempted takeover, aimed at accelerating a move away from coal-fired power, was labelled by one NSW MP from the Hunter as "environmental activism", as the federal government warned against any moves that potentially risked the reliability of the grid.

Canadian asset firm Brookfield and Mr Cannon-Brookes' Grok Ventures launched the bid before the AGL board knocked it back in an announcement to the Australian Stock Exchange.

The board said the unsolicited offer undervalued the company and was not in the best interests of shareholders.

AGL, Australia's greatest carbon emitter, plans to split into two listed entities - an energy retailer and an electricity generator - by June 30.

It would bring forward the closure of Bayswater from 2035 to 2033 and Victoria's Loy Yang A Power Station from 2048 to 2045.

Mr Cannon-Brookes told ABC Radio National the consortium had $20 billion to allow AGL to retire coal by 2030 and achieve net-zero emissions by 2035. He said he "strongly believed" the deal would result in a drop in prices for consumers, lower emissions and create more jobs than AGL's plan.

"We think our bid has significant value for shareholders and is a far better option than the alternative path, which is the demerger that's on the table, from the point of view of risk and the point of view of shareholder value," he said. "So we'll continue to work with them on that."

Federal Energy Minister Angus Taylor said energy companies had a responsibility to give consumers top priority.

"Driving out dispatchable capacity is a significant risk to electricity consumers - both in terms of reliability of the grid and electricity price impacts," he said.

"The Morrison government has been consistent and clear that dispatchable capacity must be kept in the market for as long as it is needed, and replaced with sufficient new dispatchable capacity upon retirement."

The Nationals' Upper Hunter MP Dave Layzell said he was concerned the takeover could have "unintended consequences of crashing our energy market by forcing an early loss of our baseload power".

Mr Layzell said renewable industries needed to grow alongside the Hunter's mining sector and coal-fired power stations.

"The intended takeover of AGL with the single purpose of shutting down the coal generators has some challenging implications for us all," he told the Newcastle Herald.

"[Mr Cannon-Brookes'] intended actions appear to be environmental activism instead of doing the right thing by ordinary Australians.

"Loss of energy availability is something we have forgotten about in this country but it may happen again if we are not careful. It could lead to losses of jobs, loss of businesses and even losses of industry. The social ramifications would be far reaching."

Labor's federal Hunter MP Joel Fitzgibbon said jobs, electricity prices and energy reliability were what mattered in his electorate.

"In the end, it comes down to which company can provide those three things and at this stage that is unclear," he said.

Mining and Energy Union general president Tony Maher said any bidder for AGL "better have a plan for the workforce".

"It's not good enough for decisions about the future of power stations to be made on share price alone while workers and communities are ignored," he said.

"Investors have a responsibility to the people that have kept these power stations operating for decades."

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