A former MP says Australia should consider having a one-child policy and other measures to ensure a sustainable population.

Former Upper House Democrat in South Australia, Sandra Kanck, now heads a group urging that Australia limit its population.

Ms Kanck says she knows the Catholic Church will object to her suggestion that Australia look to promoting one-child families.

She thinks the baby bonus needs to be discontinued or limited to the first child only.

The one-child limit could also be applied to paid maternity leave, she argues.

Ms Kanck says her group, Sustainable Population Australia, is worried about the strain on Australia's resources, such as water.