I just assumed it was 2/3 of a majority of sitting members. I am surprised at all the downvotes though, but I guess that is how YCombinator news works.
They'd need a 2/3 majority in the Senate as well.
The margin they have isn't even enough to get past the 60% cloture vote to pass it in the first place.
Hopefully that's where it dies - along with a lot of good legislation in the past -dead waiting for the "silent filibuster" to end.