Shellharbour MP Anna Watson has suggested the NSW government has "something to hide" by not releasing details of a $100,000 study into the Albion Park bypass.
The last state budget allocated $100,000 for a study into upgrading the Princes Highway between Yallah and Oak Flats.
Ms Watson said it was time for the government to release the results of the study.
"It's been six months and, in my view, there is absolutely no excuse for the government not to release what they've found so far.
"We want to know how much it's going to cost and we want to know how people in the community are going to have their say in the process."
Ms Watson said she was concerned that the government had not yet released the study.
"I am very sceptical about why they're not releasing this information.
"However I can only imagine they've got something to hide. Maybe they're not going to release the study due to budget constraints."
Joining her in calling for the study to be released was Keira MP and opposition roads spokesman Ryan Park.
"This is an important road project but we understand it's in an early stage," Mr Park said.
"We want to get the ball rolling so we can start to make this a priority for Illawarra residents and for those who use the road during the busy peak holiday period.
"I've said from the word go that first and foremost my priority is the Illawarra region," Mr Park said.
"That's where I come from, I'm a regional MP. I believe that regional road projects should be given just as big an importance as those in Sydney."
A spokesman for Roads Minister Duncan Gay said the review by Roads and Maritime Services (RMS) of previous studies for a proposed Albion Park bypass was ongoing.
"The investigations will help RMS to determine whether the gazetted bypass route is in the most suitable location for a future bypass of Albion Park Rail and to accommodate current road design standards," the spokesman said.
"The possible option is a long-term concept which RMS will further develop with council and the community during the planning stage, when funding becomes available."