Actually, he's talking about a not-really-ever-enforced rule that was in place back when the FEI was first opened, when it was still officially considered a "roleplay continent."
The idea was to make sure that, among other things, people didn't declare war just for game-mechanic reasons or "because we (the players) want to have some fun".
Like the rest of the "RP continent" trappings, it was abandoned because enforcement would be difficult at best, and would, effectively, require a "roleplay council" sitting in judgement over the RP lines of everyone on the continent.
