Adding a new partner to the ISS requires unanimous agreement of all existing partners. As it happens, the US is the only one who opposes China, but, in concept, any of the participating space agencies (or their controlling government(s)) could block participation.

Maybe if the other members of the international community invested as much into it, they'd get an equal say. The split is something like NASA 80%, Russia 10%, rest of world, 10%. (Although it depends how you adjust for inflation)