Thais should not take advantage of a new measure by Japan to waive visas, Foreign Minister Surapong Tovichakchaikul said on Thursday.
Mr Surapong raised concern about Thais, especially women, entering Japan as tourists to illegally work in the country.
"If they want to work in Japan, they should go through a legal channel, not work illegally,'' said Mr Surapong, who also is a deputy prime minister.
The Japanese government on Tuesday approved a measure to lift visas for tourists from Thailand and Malaysia to boost the tourism sector. The step will be implemented this summer but the launch date has not been announced. Summer in Japan runs from this month to August.
The minister said he was afraid that Japan might revert to a visa fee for Thais if they overstay in Japan, now one of the most popular destinations for tourists from Thailand.
New Zealand lifted its 30-day visa-free policy for Thais after finding that many Thai women went there as tourists and worked illegally in the country.