These are two Ganking Guilds teamed up, a horde one and alliance one, called Merciless Midgets and Mercy to Midgets. They are on another server, but what they are doing is still lame. Its pretty much flat out extortion.
They talk together in an outside voice program like ventrillo and set up "toll booths" at bridges throughout the world.
If an Alliance comes up, he has to pay the Alliance members gold to cross the bridge, or the horde gank him. If a horde comes up he has to pay the horde or the alliance do the same.
And here in GM discussions. The GMs say that it's ok and they arent doing anything wrong. http://www.mercilessmidgets.com/mercilessmasters.htm
Kinda lame if you ask me.
Added: just read that while the ganking is going on, which ever faction is the same as the one being attacked constantly spams the trade window to hinder their ability to fight back.
Fucking lame.