There are multiple laws in the game that are contradictory to each other. If you pass one law in the council, the other law gets repealed. That's what this achievement is about.
For example, let's do it with the "parenthood" law.
Go to idea tree -> society -> parenthood. Research "Communal parenthood", and once complete, pass the law in council.
Again go to idea tree -> society -> parenthood. Research "Dedicated parenthood" (or something like that. I forgot the exact name), and once complete, pass the law in council.
I think this is when the achievement will pop. If not, wait for next council meeting and again pass the "Communal parenthood". Definitely will pop now.