This achievement can be obtained in the Conveyor Hub sub-area within Central Production B. To obtain it, you must kill the four enemies gathered around the Iron Maus vending machine in a remote corner of the map.
After entering the Conveyor Hub for the first time and encountering the first rocket launcher, you'll come upon some stairs that lead down. On the left on a raised platform is another rocket launcher, while to the right is an open area with a new type of robot enemy. To the right of that robot is a wide set of stairs leading up to an area with shipping containers and cargo boxes. The Vending Machine Cult is in that room.