That precedent already exists. Trespassing planes were shot down during the cold war, when they could be, and China knocked a US intelligence plane out of the sky over "contested" airspace (way south of China, near some of the islands they're claiming in a move to gain sovereignty over as much of the sea route via the Straight of Malacca, and sea routes to SE Asian states like Vietnam, as they can) in '01 (kinda by accident, probably, but that didn't stop them from claiming it was OK for them to do that and detaining the flight crew until an apology was issued)