It does not.
It has; in my 5 years on the SC there was never a vote where only 3 people participated that I can remember.
Plus I think there would be major yelling from the rooftops if two people got elected to any of these councils who put their employer before the community. So I personally don’t think such a rule is necessary due to other safeguards such as being able to have council members tossed out if they turn out to act in bad faith.