From Command and Conquer Wiki

EMP Control Centers are battle stations located in Yellow zone cities that are designed to launch EMP attacks shutting down structures and vehicles alike. They are easily distinguishable by their four cylindrical towers extending into the sky.

These structures were constructed as the first lines of defence against Nod aggression. In theory, a volunteer crew would race to the EMP Control Center as the first wave of attackers is seen and fire the EMP immobilizing them, giving time for civilians to evacuate and any military forces in the area to quickly respond. In practice, the system never worked, as Nod became dormant and the volunteers eventually lost their fervor.

Today, these structures are still in operational shape, but are abandoned and will serve anyone willing to take control of them.