Bidders for the lease of the NSW “poles and wires” will have to sign a guarantee that electricity prices will be cheaper in five years, Premier Mike Baird says.

“The transaction will not go ahead on the basis of prices going up,” Mr Baird said on Sunday, with Prime Minister Tony Abbott and Treasurer Joe Hockey at his side.

“They will only go ahead on the basis the transaction puts no upward pressure on prices, downward pressure comes.”

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To enforce the price guarantee, Mr Baird named former ACCC chief Allan Fels as the state’s new electricity price commissioner.

Companies that buy into the network will have to give the commissioner an annual update on their compliance with the guarantee.

Under the coalition’s “poles and wires” proposal – which it is taking to the March 28 election – 49 per cent of NSW’s electricity distribution network will be sold and is expected to raise a windfall that could unlock $20 billion, including interest and $2 billion in federal funding.

The money, he says, would be spent on roads, rail, education and health.

Unions have been running a large campaign against the sale, but Mr Baird said their opposition was restricting infrastructure development.

“The unions need to stop their dishonest campaigns,” he said.