Mr Cahill said three of those arrested today were identified as high level offenders during Operation Ark.
Their alleged repeat drug offending was brazen, he said.
"That's why we were pretty keen to target them and shut them down again.
"They changed the way they were operating a bit but they still maintained their roles of overseeing the importation of the drugs."
All four of the alleged repeat offenders have name suppression.
Mr Cahill said the charges levelled today better reflected the gravity of the crimes carried out by the alleged offenders.
Police would oppose bail being granted again, he said.
"We're completely disappointed that they showed a lack of regard for the law - with the way they thought they could continue to offend."
Mr Cahill said the "designer drug ring" targeted in today's operation was importing ecstasy-type pills in powder form from China and Singapore.
The ring made millions of dollars in sales, with one dealer alone purchasing $4.5 million of pills from an importer, Mr Cahill said.
"There is a lot of ignorance amongst users of these drugs, about what the pills contain and the level of danger associated with using them," he said.
"Today's activity will have an impact on the supply of harmful drugs that are regularly leading to hospital admissions."
About $100,000 and four motor vehicles were seized, along with several thousand drug pills and 3kg of ingredients for making pills.
