Prime Minister Julia Gillard's attempt to decouple the issues of immigration and population growth is ridiculous, the federal opposition says.
Asked on Wednesday if she would cut immigration to ensure a sustainable population, Ms Gillard said the debate was about planning and policy choices for the nation's future growth.
But opposition immigration spokesman Scott Morrison said the two issues are inseparable.
"She made the ridiculous statement that immigration has nothing to do with curtailing population growth," Mr Morrison told reporters on Wednesday in Sydney.
"She says she wants to do something about sustainable population but she doesn't want to address the primary reason that population is growing so significantly.
"And any prime minister who says they want to do something about getting population growth under control obviously has to address immigration."
Australia's immigration rate is the main reason the population is forecast to reach 36 million by 2050. Ms Gillard does not support such a number.
"I don't believe that this is an immigration debate ... I believe it's a debate about planning and policy choices for the nation's future, about where we want to see growth," she told reporters in Sydney.
"We do need skilled migrants, definitely."
Meanwhile, another boatload of asylum seekers has been intercepted near Christmas Island, with about 40 people on board.
It is the first boat to arrive since the federal election campaign began on Saturday.
It was the 80th suspected illegal entry vessel to arrive in Australia this calendar year, Mr Morrison said.