CABRAMATTA MP Nick Lalich and Opposition energy spokesman Ron Hoenig said the state government had increased gas prices by nearly 18 per cent.
Mr Hoenig said that from July 1, local families could expect to pay 17.8 per cent more for gas.
He said the average annual household gas bill had increased from $576.75 in 2010/11 to $1228.75.
"Families are already struggling with the rising cost of living under the Liberals," Mr Hoenig said.
"The last thing people in south-western Sydney need are more price hikes for essential utilities."
Energy Minister Anthony Roberts said on June 10 the Independent Pricing and Regulatory Tribunal had determined an average increase to the regulated retail gas price of 17.7 per cent over two years.
"This will affect the fewer than 25 per cent of NSW gas customers who remain on the regulated price and I encourage customers to shop around to make sure they are getting the best deal possible," Mr Roberts said.
He said the state government made a strong submission to IPART.
"As a result of the government's submission, the price set by IPART is up to 7 per cent lower than what was originally proposed by gas retailers.
The opposition MPs also expressed concern about electricity prices.
Mr Lalich that said from July 1 electricity providers were no longer subject to a cap on prices, after the state government removed the maximum amount retail electricity providers could charge.
"We're now seeing that trend continue, with gas prices rising by 17.8 per cent and the cap on electricity prices going by the wayside," he said.