Allies could have a diplomatic option to create some an Union. This Union can create laws that are imposed to all allies. These laws would have to be voted by all the allies to be validated. You can have the option to bribe an ally so that he can vote for your prefered law (AI will have a bribe threshold while a human player would need to specify the ammount he wants).


Such laws could be a more strict penalty for alliance breakup, all trades more focused on science, etc.


The Union must have a Union leader that is periodically voted among the allies. Bribes can also happen at this stage. An Union leader has two votes when voting on laws and gains a bonus in Influence.