Duterte said he was concerned that a lot of Drugs had arrived in the Philippines via Taiwan. That was the official reason.
huge drugs bust named 2 Taiwanese as involved
"Two Taiwanese—“Jun Wang” and “Jhu Ming Jyun”—wanted to rent his sister’s old house for use as a “bodega,” and they wanted someone whome Emily trusts to be the warehouseman.
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Visa-free trial period for Filipinos has apparently been extended until July 31, 2019:
http://www.taipeitimes.com/News/taiwan/archives/2018/06/29/2003695770
Guy