Idea for how legislation in supranational unions could work

I’ve seen a lot of people propose unions of countries and a lot of them propose that countries could decide and vote on legislation, which you’ve already said is not something you want to do, which is why I think maybe an EU Parliament style of legislature could be better.

Like European elections, I think unions’ elections should be run in each country individually, kinda like just a normal election, to elect the amount of seats their country is allocated (it could be standard for all countries or it could be based on population). Parties should usually try to join union-level parties. For example, in a union between Country A, Country B and Country C:

• People’s Party includes National Rally from Country A, Republican Conservatives from Country A, People’s Alliance from Country B and the Conservative Party from Country C

• Socialist Alliance includes Social Democrats from Country A, Socialist Party from Country B, and Workers’ Socialist Party from Country C

• Workers’ Federation includes Workers’ Party from Country A, Communist Party from Country B, Workers’ Union from Country B and Communist Party from Country C

These parties would function like federations. I could see 2 ways of this being implemented:

• 1: For every piece of legislation, every member party votes on how the union-level party should vote together. Same for proposed legislation, where every member party can propose legislation for the union-level party to propose.

• 2: Every year maybe (early elections could be called if member parties want to or if the leader party disbands), member parties vote on who should become a leader party from a selection of parties that decided to be candidates. The party that becomes the leader party essentially represents the party and is the party in every way that matters.

Not every national-level party has to subscribe to a union-level party. If you’re looking at a parliament chart, parties that aren’t members of any union-level party are shown as ‘Non-inscrits’, like in the EU.
I think there should be an option in the parliament chart to either see union-level parties or just see the national-level parties individually.