They face charges connected to the alleged importation of ecstasy and mephedrone from suppliers in China and other countries.
Two of the suspects are also accused of money laundering offences as part of the same inquiry.
Charges were brought by the Serious Organised Crime Agency (SOCA) following the seizure of thousands of tablets in Belfast this week.
One of the Agency's senior officers told the city's Magistrates' Court contact has been made with countries worldwide.
Appearing in the dock were: Ryan McManus, 29, of Empire Street, Belfast; Ryan Milligan, 27, from Manse Road, Dundrum; and Connor Devenney, 34, of Dunwellan Park, Newcastle, Co Down.
All three are jointly charged with conspiring to fraudulently evade the prohibition on importing Class A drugs, namely ecstasy, into Northern Ireland.
McManus and Milligan both face further charges of transferring criminal property and conspiracy to fraudulently evade the prohibition on importing Class B drugs, namely mephedrone.
Devenney is also accused of possessing cannabis with intent to supply.
The case is understood to have been brought by SOCA due to the alleged sending of parcels through the postal system.
The Agency has the powers of a police constable, customs official and immigration officer.
It was claimed in court on Wednesday that surveillance evidence forms part of its case against the accused.
During questioning by the defence the officer was asked if it was a global investigation.
"It has international connections," he replied.
"Contact has been made with several jurisdictions throughout the world."
Milligan and McManus did not apply for bail and were remanded in custody to appear again on 23 August.
Devenney is to be released if an approved address can be found.
Ordering him to report to police three times a week, District Judge Fiona Bagnall also imposed a ban on using the internet.
Devenney is due back in court on 4 September.