Deputy Public Health Minister Sathit Pitutecha said health authorities have the identities and contact details of this group of passengers, which can be used to track them down.
If they don't cooperate, they will be arrested and face a one-year jail term and a fine of 200,000 THB (6,330 USD), he said.
Thailand has introduced new screening process in which all Thai and foreign passengers from the RoK must come to initial health checkpoints to be questioned and divided into groups of monitoring.
Illegal workers with travel history to Daegu and North Gyeongsang will be quarantined at a navy facility in Chon Buri's Sattahip district.
Those with less risk will be sent to regional screening venues to determine if they should be placed in state-designated quarantine venues, or sent home for self-quarantine.
Other passengers will be advised to go into a 14-day self-quarantine and required to report their condition to health officials every day.
The added screening and health reporting requirements are also applied to those coming from other high-risk zones announced by the Thai Ministry of Health, namely China, Hong Kong (China), Macau (China), Italy and Iran.
According to the Thai Foreign Ministry, the RoK Immigration Office informed the Thai embassy in Seoul that more than 5,000 Thais reported themselves to the office from December last year to March 1.
Media reported that the number of illegal Thai workers in the RoK may reach at least 140,000 while only 20,000 work legally.
Thailand has so far confirmed 50 COVID-19 infections, including one confirmed death./.VNA