Suppression towers are Purifier structures. They were designed to protect Purifier facilities. During the End War, when a facility was taken over by a Tal'darim AI personality, these towers were used to stall Aurana's progress in purging the AI from the facility.
Suppression towers appear in the "Malwarfare" map in Co-op Missions. They will strike at Aurana's transport and interrupt the timer on the objective. When the towers spawn, they will be surrounded by enemy units. The towers will attack units around them, lowering the attack speed of whatever they hit with their beams. These attacks are telegraphed, and can be moved out of.