Some of the largest employers of NSW were secretly planning to flee the state after their power and gas bills soared up to 50 per cent, it has been revealed.

Steel, construction, manufacturing and mining businesses are tired of successive governments that have not handed over an efficient power grid, The Daily Telegraph reported.

Energy Markets Reform Forum spokesman Bob Lim, who represents dozens of big energy users including Tomago Aluminium, VISY, Bluescope Steel, Kimberly-Clark and OneSteel, said forecast hikes in electricity, gas and water bills have forced big firms to look elsewhere and scale back their operations in NSW.

He warned the long-term impact on the NSW economy will be severe as companies seek overseas and interstate options before an emissions trading scheme is introduced.

Job losses and the closure of factories are a reality, Mr Kin said. Last year, OneSteel and Bluescope Steel discharged hundreds of jobs and slashed production in NSW.

Opposition energy spokesman Duncan Gay said he would not be shocked if large companies left NSW after being forced to bankroll an overdue energy infrastructure upgrade.

"NSW Labor has ripped nearly $14 billion out of the state's energy retailers in dividends and taxes and failed to re-invest this in our ageing infrastructure," he said.

Meanwhile, Queensland Treasurer Andrew Fraser said he would welcome NSW companies.