It was triggered by the shooting by members of the Philippine Coast Guard of a Taiwanese fishing vessel in the overlapping maritime borders between the Philippines and Taiwan in the Balintang Channel off Batanes on May 9, 2013. A Taiwanese fisherman, 65-year-old Hung Shih-cheng, was killed.
The Aquino government took the defensive position right away insisting that the Taiwanese vessel intruded into Philippine waters.
It was established that the incident happened 21.6 nautical miles from Batanes, not within the Philippine 12 nautical miles territorial waters but within the 200 NM economic exclusive zone. But at the same time it is 170 nautical miles from the southernmost point of Taiwan and still considered within its 200 EEZ.
International law provides the rules of engagement in overlapping EEZs. Shooting is never one of them.