The Bank said there were shops in Tongatapu and the outer islands offering unlicensed foreign exchange services, including cash conversion.
Only dealers authorized by the Reserve Bank are allowed to move money in and out of Tonga.
“Providing foreign exchange services without the required license is an offence,” the Bank said.
Illegal dealers have been warned to immediately stop what they were doing.
The Reserve Bank warns that Individuals face three years in prison and fines of up to TP$20,000.
Fines for companies breaking the foreign currency regulations are up to TP$200,000.
Illegal transfers cannot be monitored or taxed and money may not be changed at the legal rate.
According to a World Bank report Tonga on 2016, Tonga was the Pacific country most dependent on money sent home by Tongans working overseas.
The report said remittances made up nearly 33 percent of Tonga’s GDP in 2015.
About 12,000 Tongans work in Australia and New Zealand under seasonal employment schemes.