The White House earlier this month reaffirmed its stance that the Taiwan Strait constitutes "international waters" following the latest US warship sail-through, which had put China's PLA Eastern Theatre Command on high alert. As Reuters reported last Tuesday, "The United States on Tuesday backed Taiwan's assertion that the strait separating the island from China is an international waterway, a further rebuff to Beijing's claim to exercise sovereignty over the strategic passage."
This prompted Beijing to issue its own statement and definition, hitting back that the strait is not "international waters" - thus placing limits on the movements of foreign military vessels in the waters - and further reasserting that it constitutes the mainland's exclusive economic zone.
Bloomberg reports Monday that Biden administration officials are "increasingly concerned the stance could result in more frequent challenges at sea for the democratically governed island, according to people familiar with the matter."
And further, "Chinese officials have made such remarks repeatedly in meetings with US counterparts in recent months, Bloomberg reported last week." The report underscores that this marks an escalation, given the international legal status of the passageway wasn't previously center of debate as it is now:
While China regularly protests US military moves in the Taiwan Strait, the legal status of the waters previously wasn’t a regular talking point in meetings with American officials.
Washington is alarmed over the timing, not only given the ongoing fallout from the Russian war in Ukraine, which Beijing has refused to outright condemn, but especially because a week ago China's President Xi Jinping has signed an order which fundamentally expands the conditions under which People's Liberation Army (PLA) troops can be deployed.
The order introduced legal framework to deploy troops in "non-war military actions" which took effect Wednesday, according to state media. It could have significant repercussions for tensions with the US and Washington allies like Australia or Japan in places like the South China Sea and the Taiwan Strait, given the order loosens the conditions under which it's possible to initiate "military operations other than war" which involves operations that do not explicitly involve direct conflict or combat.
Depending on how far China wants to press its definition, the most extreme scenario could involve the PLA military moving to close the strait...
This further means that Xi is hinting he could use the PLA military to begin enforcing the newly articulated position that the Taiwan Strait is not "international waters" - however vague the Chinese position may remain.