The warning was carried on new signs posted at Bangkok's Suvarnabhumi airport.
The Suvarnabhumi Airport Passenger Control Customs Bureau will calculate the value of all personal items - souvenirs, gifts or brandname goods - purchased overseas. If the combined value of those products exceed 10,000 baht, passengers and airline crew will have to pay import duty.
Signs announcing enforcement of the limit were placed at the airport, explaining that "personal goods" includes new clothes, shoes, socks and bags in non-commercial form.
If goods being brought into Thailand exceed the limit, they must be declared to customs officials and the duty paid before their baggage go through the X-ray machine. Any undeclared items will be seized and the owners may have to pay up to four times of the value including plus the duty.
The department said food, food supplements and cosmetic will not get the duty waiver. Travellers are limited to 200 duty free cigarettes and one litre of duty free liquor or wine.
Gifts prepared to give to other people, donated items, collectable items, second-hand goods, empty watch and brandname bag boxes are not considered as personal items. Individuals bringing in these products have to inform customs officials before the baggage X-ray.
Expensive new watches or bags worth more than 10,000 baht will be liable to duty, even if being worn.
Somchai Asawadtriratanakul, the bureau’s chief of investigation and suppression division, said the regulation was an existing one, but enforcement will be stricter. The bureau found many people brought in new products for resale in Thailand without paying import duty. Action had to be taken to prevent this.
Initially, signs were posted at arrival and departure areas. If duty-payable goods are found undeclared in possession of a passenger who refuses to allow the goods to be seized, the case will go to court, he said.
If the passenger loses the case, the smuggled goods will be seized and they would be liable to a fine of four times the assessed value, including the import duty, and/or a prison term of up to 10 years.