Prime Minister Malcolm Turnbull has seized on the 28th turnback of an asylum-seeker boat to warn Australia can't risk Labor giving people smugglers an inch.
The government on Wednesday revealed the navy earlier in June had intercepted a boat carrying 21 people from Vietnam.
All onboard were returned to Vietnam.
In an attempt to switch the campaign focus from Labor claims about a secret coalition plan to privatise Medicare, Mr Turnbull ramped up the rhetoric on border security during a visit to Cairns.
He accused Labor leader Bill Shorten of lacking the will to turn back boats.
"The people smugglers will continue to test our resolve," Mr Turnbull said.
"The only thing that is stopping it is the steely resolve of my government."
The challenge was greater than it's ever been because people smugglers used social media to market their trade, Mr Turnbull said.
"You cannot give an inch to the people smugglers - they are determined criminals.
Mr Shorten insists Labor has the same policy as the coalition to deter people smugglers.
"You have to love the Liberal Party central headquarters. It is the break-glass issue," he told reporters in Sydney.
"They should be ashamed of themselves, giving the business model of people smugglers a jolt in the arm by playing tawdry partisan politics."
But Immigration Minister Peter Dutton warned Australians could not be complacent.
"People who think this problem has gone away, please don't believe that," he said, pointing to the humanitarian crisis in Europe and the Mediterranean Sea.
A UN refugee agency report released this week put the number of displaced people, refugees and asylum seekers worldwide at more than 65 million.
"Potentially (they) could come to a country like our's tomorrow," Mr Dutton said.
The minister denied the coalition was playing politics by using boat arrivals in Australian waters during the election campaign.
He attacked Labor's policy to remove temporary protection visas from asylum seekers already in Australia, saying another 14,000 were ready to get on boats from Indonesia.
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