Any one member, either party. However, word is that House GOP leadership and the Freedom Caucus have been negotiating some rules changes that would include increasing the threshold.
I'm pretty sure they can get 9 Democrats to call for a vote. That rule is probably just to keep rabble rousers on their own side (like Matt Gaetz) from causing trouble and forcing a vote. Marjorie Taylor Greene is a likely suspect if I were to bet on anyone from their side trying.
Comments
Plans are in the works to increase the threshold for a motion to vacate the chair to any 9 members.