The Secretary of Foreign Affairs in Tonga says Air New Zealand has apologised for allowing people into the country without valid entry visas.
Fekita 'Utoikamanu says the airline brought two Czech nationals into the country without checking their documents properly.
The men were detained overnight at Fua'amotu International Airport and spent a second night at the home of the local Air New Zealand manager before being flown back to New Zealand.
Ms 'Utoikamanu says the airline has been warned that it will be fined more than 3-thousand US dollars if the incident is repeated.
She says it is the third time the airline had made the mistake in the last month.
Ms 'Utoikamanu says the apparent oversight should not have occurred.
"We issue a list of countries that do not require a visa prior to boarding the flight to Tonga, and that list is on the web so there should not be a misunderstanding of which countries are allowed in and which countries need to get visas prior to arrival"