Liberal senator Jim Molan says Australia may have already reached its sustainable legal immigration limit.
New Liberal senator Jim Molan has warned Australia's culture and infrastructure may not be able to handle any more legal migration.
The retired major general made his first speech in parliament on Wednesday, following a controversial start to his political career.
"I am concerned that the level of legal migration, now that we control our borders, is in excess of the capacity for our cities to absorb, both culturally or in terms of infrastructure," Senator Molan said.
"We are approaching limits on this, if we have not already exceeded them. I don't have the answer, but I certainly have the concern."
Last week, Senator Molan was accused of racism - which he strongly denied - and war crimes, with the latter charge eliciting two apologies from Greens MP Adam Bandt.
He said he was hopeful his speech could provide context.
"If opponents don't speak against you, you probably are not standing up for enough," he said.
Senator Molan, a co-author of 'Operation Sovereign Borders', said he was proud to have been involved in one of the most successful and humane approaches to immigration policy.
After a 40-year military career, which included a year as chief of operations for the US-led coalition in Iraq, the NSW senator intends to make defence a key focus.
The 67-year-old believes Australia must increase its strategic self-reliance.
"I have no expectation that governments immediately spend one more dollar on defence, but for years I have advocated that we must be more open about the strategic risks that are being taken in the name of the Australian people," he said.
Senator Molan took the seat of former Nationals deputy leader Fiona Nash, who was ruled ineligible by the High Court for holding dual citizenship.
Liberal Hollie Hughes was in line to replace Ms Nash but she was found to be disqualified because of her job with the Administrative Appeals Tribunal.
The sequence of events prompted an admission he shared a parallel with Olympic gold medallist Steven Bradbury.
Senator Molan said journalists who described him as a member of the NSW hard-right hadn't met a member of that group, insisting he has no factional alliance.
But he did note his contact with prominent conservatives John Howard, Tony Abbott, Scott Morrison, Peter Dutton, Concetta Fierravanti-Wells and Stuart Robert.
He finished with the most important determinant of himself - the Australian military.
"To me, they represent everything that is good about Australia - because they are Australia."