The NSW government is moving to put up 49 per cent of the electricity network for lease and has pledged to invest $20 billion in infrastructure for the state.

However, reports emerged on Tuesday that NSW Treasury officials said spending the proceeds of the lease on infrastructure would cost the budget $1.5 billion a year.

The union movement is opposed to the leasing of the network, largely because of concerns of massive job losses in the electricity sector.

Unions NSW Secretary Mark Lennon said this news showed the long-term budgetary problems that would arise from the leasing.

He highlighted the fact the network brought in $1.4 billion to the public coffers in the 2013-14 financial year and any leasing would mean the state would forgo almost half of that.

Mr Lennon was also concerned at the lack of investment in crucial services.

"The loss of long-term revenue from these assets for a short-term sugar hit will mean a decline in the quality of health, education and transport services to the people of NSW," Mr Lennon said.

"We are not against impressive new infrastructure builds, but just as important as the showy stuff is investment in our schools, our hospitals, and our emergency services."

He highlighted the need to invest in TAFE, because the budget papers showed 30,000 fewer students were enrolling this year.

Premier Mike Baird was asked about the $1.5 billion claim in Parliament this week by Opposition Leader Luke Foley.

Mr Baird disputed the suggestion the electricity network brought in that much money.

"If members of the opposition actually read the budget papers, they would be able to see the dividends in 2015-16," Mr Baird said.

"Dividends and tax equivalent payments amount to $463 million in 2015-16; in 2018-19 they will be $224 million."

Mr Baird did admit that up to 2024, "revenue will be lost".

"But the expectation, in the modelling that has been done independently by Deloittes, is that the economy will grow," Mr Baird said.