Using the results of a free doctor-referred coronavirus test to travel is punishable by law, the Health Board has said.
The agency has noticed people are asking for referrals from the doctor to get tested for free and then use the results to go on holiday.
A free test is meant only for people who have coronavirus symptoms or are a close contact. If a person wants to travel abroad they must pay for their own test.
When test results are checked at the airport it is possible to see if the traveler was referred for a free test by the doctor or if they paid for their test themselves, the Health Board said.
The agency said if a person is caught doing this they can be detained or fined.
The Health Board and Police and Border Guard Board regularly check travelers' test certificates at the border.
Editor: Helen Wright