http://classic.particracy.net/viewbill. ... 1&vote=yes
Votes: This bill proposes the withdrawal from a treaty. It will require half of the legislature to vote in favor[?]. This bill will not pass any sooner than the deadline.
The bill in question does, indeed, withdraw from a treaty. But it simultaneously ratifies a different treaty - my understanding is that the higher threshold should control, so this law _should_ require 2/3s, due to the ratification in Article I.