The number of Vietnamese visiting Taiwan reached more than 37,000 in July and August each but the figure fell to 30,000 in September and 32,000 in October, Taiwan News reported citing the Tourism Administration of the Ministry of Transport.
Travel agencies blamed the decline for the strict visa change by Taiwanese authorities.
Starting from mid-September, Vietnamese citizens who hold Japanese and South Korean visas were no longer automatically eligible for obtaining Taiwan's Travel Authorization Certificate, known as a multiple-entry visa valid for three months, allowing single stays of up to 30 days.
With Taiwan's new regulation, those holding Japanese and South Korean visas will have to apply for Taiwanese visas as normal, which take eight days for approval.
The longer visa processing period has dissuaded some travelers from visiting the island, according to a Focus Taiwan report.
In recent years, Vietnam has been among the biggest feeder markets for Taiwan's tourism.
In 2019, the year before the onset of Covid-19, Taiwan welcomed over 777,000 Vietnamese tourists, a year-on-year increase of over 26.5%.