Nearly 200 passengers on an August 25 flight from the Greek island of Zante to Cardiff have to self isolate after sixteen people tested positive for COVID-19.
Public Health Wales originally said that at least seven passengers were infected with virus from different parties while onboard TUI Flight 6215.
"These passengers will be contacted shortly, but meanwhile, they must self-isolate at home as they may become infectious, even without developing symptoms. Anyone with symptoms should book a test without delay," said Dr Giri Shankar, the incident director for the COVID-19 outbreak response at Public Health Wales.
Shankar said that all passengers on board the flight would be considered close contacts.
"At the request of Public Health Wales, we have contacted all passengers who were on board TOM6215 from Zante to Cardiff on 25th August," a spokesperson for TUI said in a statement provided to Euronews.
One passenger on the flight, Stephanie Whitfield, told the BBC that not everyone was wearing a mask correctly but that staff did not correct all passengers.
"Passengers are informed prior to travel and via PA announcements on the flight that they have to wear masks throughout and are not allowed to move around the cabin," the TUI spokesperson said.
"Masks can only be removed when consuming food and drink. A full investigation is now underway as these concerns weren’t reported during the flight or before today."
Many social media users lashed out at the travel company on social media stating that they planned to cancel their holiday over the incident, whereas other users said that people shouldn't be risking international travel during the pandemic.
Greece is currently part of the just over 60 countries exempt from Wales' 14-day self-isolation policy for international travel.
There are more than 10,000 cases of COVID-19 in Greece, more than half of which were reported this month.
Passengers from some countries arriving in Greece are required to have tested negative for COVID-19 up to 72 hours before their entry to Greece.
Face masks are now mandatory indoors and outdoors on the island of Zante and gatherings are limited to nine people.