Opposition Leader Tony Abbott said a $1 billion blowout in border protection costs had meant cuts to cargo screenings.
"Border protection failures on boats are now leading to border protection failure on guns," he told the lower house on Wednesday.
"There have been enormous cuts to screening as a result of the blowout in border protection costs.
"Since 2010, 340 staff have been axed from customs and border protection.
"The budget of customs for cargo screening has been decreased. It's been cut by almost $60 million."
Mr Abbott said that had resulted in a 75 per cent cut to air cargo screening and a 25 per cent cut to sea cargo screening.
"Is it any wonder that illegal guns are coming into this country?" he said.
On Tuesday, an international trafficking operation supplying black-market guns from Germany to criminals in Sydney was smashed by NSW police strike force Maxworthy.
Four people were arrested in Sydney, of whom three were charged, following raids in Sydney and Remscheid, Germany. One person has also been arrested in Germany.
The raids involved NSW Police, Australian Federal Police, Customs and Border Protection Service, the Australia Post Corporate Security Group and police in Germany.
Opposition immigration spokesman Scott Morrison said the revelation that guns were being illegally imported was bad enough.
"The fact that the guns, though, have been allegedly used in the drive-by shootings that have plagued Sydney is even worse," he said in parliament, adding there had been 60 shootings in Sydney in the year to February.
Mr Morrison said customs did not even know about the handgun trafficking until the NSW police investigated.
"If you can bring (in) components of Glocks, then what other components are being brought in for even more serious weaponry across our borders to threaten our national security?" he said.
Home Affairs Minister Jason Clare said the syndicate was cracked after NSW police seized a Glock handgun in Wiley Park, Sydney.
He told parliament it was traced by the Australian Crime Commission (ACC) back to the factory in Austria and from there to a dealer in Germany, and subsequently to the ring in Sydney.
Mr Clare said the commonwealth was working closely with state and territory governments on the problem of illegal firearms, and the ACC had been directed to make it a top priority.
"That will lead to a presentation of this criminal intelligence information to a meeting of attorney-generals next month and will lead to a recommendation to police ministers when they meet in July," he said.
Mr Clare said it was a bit rich that the opposition was talking about cuts to customs when the coalition wanted to get rid of 12,000 public servants if it won government.