If they are Australian citizens they can not easily be deported....

If they are Australian citizens they can not easily be deported. If, however, they are the same as that Maltese born bikie thug whose parents never had the sense to take out Australian citizenship (or maybe never had the desire to do so) then it would be relatively easy to do so

Not welcome: Rebels bikie gang leader Alex Vella stranded in Malta as Australian visa blocked

Neil Doorley, The Courier-Mail
June 16, 2014 10:00p

"AUSTRALIA’S largest motorcycle gang, the Rebels, is in turmoil after the Federal Government moved to stop long-serving national president Alex Vella from re-entering the country.

Sydney-based Vella – known as the Maltese Falcon – had been on vacation in Malta when authorities cancelled his visa.

Immigration Minister Scott Morrison confirmed the move had been taken last Friday “under character provisions of the Migration Act.

Vella, a millionaire former boxer, has been living in Australia since the 1960s but is understood to have never applied for Australian citizenship."