Should neither candidate for president get to 270 votes in the electoral college, the twelfth amendment to the constitution specifies that the House of Representatives "shall choose immediately" a new president, but with one vote for each state.
Should one party have serious issues with that candidate, and assuming they control the majority in the "normal" House, could they block this process? What happens if they decide to not schedule this vote in the House's agenda, despite the constitution specifically obligating them to immediately do this vote?
My first guess would have been that the "en bloc" House could set the agenda for this one vote themselves. The issue is that "a quorum for [the] purpose [of this vote] shall consist of a member or members from two-thirds of the states", so if both parties have at least one member in two-thirds of the states, both parties can form this quorum, and validly vote in their preferred president without members of the opposite party present. As this is absurd, clearly the location and time of this vote should be decided by another authority instead. Is this other authority the "normal" House?