Taiwan joined the World Trade Organization on its own accord a couple of years ago. It negotiated its own treaty and with the global body for its admission and full membership of the organization. Earlier this year, China demanded the WTO Secretariat downgrade Taiwan's English Title from "Permament Mission" to "Trade Office", on par with that of Hong Kong and Macau. This is, of course, intolerable to Taiwan.
Taiwan is not a part of China and its accession to the WTO was not done in the way that of Hong Kong and Macau (both colonies of Britain and Portugal and the time of their accessions). Taiwan joined the WTO as an EQUAL to any other state that is a member of the organization. A treaty was signed between the two which neither side has the right to unilaterally abrogate.
It is self-evident that China, as usual, is in the wrong. They have no right to force Taiwan to change its status unilaterally. Their attempts to do so only show the insincerity of Beijing and their lack of regard for the rule of law.
Links:
WTO Secretariat's demands offbase
Ministry Takes WTO Fight to Geneva
WTO Chief meets with Yen over dispute
Editorial about China's tricks in the WHO and WTO