After recieving many complaints, the admins have made the following decision:
You CAN coordinate with your registered allies and guild members to attack a mage.
AFTER you finish attacking a mage, you CAN message non-allied mages suggesting they take their counter too. If you continue attacking after a non-allied mage counters, it may be considered illegal guilding.
You MAY NOT reveal stacks or other info about a mage to non-allies.
You MAY NOT discuss bbq times or otherwise plan counters with non-allies.