MANY people don't understand an airport at Badgerys Creek would just be a fall-back option during the Mascot airport curfew, says Fowler MP Chris Hayes (Labor).
"The majority of people travelling to Australia will still want to come to Sydney," he said.
"So an airport at Badgerys Creek would just be picking up the overflow of planes from when Mascot is closed between 11pm and 6am.
"There's no doubt it will be a 24-hour airport.
"People will just be coming here in the midnight hour, so that won't boost this area's economy or do much for tourism.
"Of course, creating employment is important but it isn't clear that an airport would actually bring thousands of jobs."
Mr Hayes recently addressed federal parliament about the airport and said the federal government should learn from the Victorian state government's experience with Avalon airport.
He said that airport "is a salutary warning that there's no guarantee a second Sydney airport, wherever it's located, would be financially viable over the longer term".
Werriwa MP Laurie Ferguson (also Labor) was also opposed to an around-the-clock airport.
"Why should residents have to endure the disruption to their life 24 hours a day when there are curfew's in other areas?" he asked. "There's no evidence the airport would provide the jobs because we don't know a lot about the plans.
"There's very strong public opposition to this in the community and I have no doubt they will come out intensely against it."
Despite the opposition of local MPs, including Liberal Macarthur MP Russell Matheson, Prime Minister Tony Abbott is expected to announce this year that a second Sydney airport will be built at Badgerys Creek.
It is believed that the first allocation of funding of the airport project will be provided in the 2014-15 budget, which is due to be released in May.