Is account stacking bannable?

Hi, I'm currently on 500 player map, and of course there are some players who are just being unfair and making more than one account and then taking that account resources and land with their main account, that feels unfair! You can see in top by provinces, there is like 2 or 3 who are definitely doing it, cause its not just by luck few provinces, but 10+ in first 2 days without losing anything, and that is just annoying and unfair and should be punishable! Is it? can I somehow report those "lovely" lads?

Not even one day has passed and this is happening, like how is this fair?