The Trade Union is a building which provides bonuses to production buildings within range, based on items being equipped into its three item slots.
How to use
When placing a Trade Union, a circle will be shown in a wide radius around the building, indicating which production buildings will be affected by the items placed within it. A Trade Union effect range cannot overlap that of another Trade Union, limiting item effects to a maximum of three per production building. Until items are placed into the item slots of a Trade Union, the building itself will have no effect.
Once placed, clicking on the Trade Union will bring up three empty item slots. Clicking on one of these item slots allows the player to select an item from those currently available in the Items tab of that island's warehouses. Once an item is socketed, it can be removed by right-clicking the item, which will place it back into the island's warehouse item storage. Certain items can be activated by left clicking them once socketed, and will provide their bonus for a specific duration (typically being destroyed after use).
After being built, selecting the Trade Union will highlight all buildings to which it is currently applying an item effect. When building production buildings within range of a Trade Union, the Trade Union will display a light outline to indicate it is within range to provide item effects.
Items which can be slotted into a Trade Union can have many different effects on production for affected buildings, including but not limited to:
- Increased productivity
- Changing the required goods required by a production building
- Reducing the workforce required
- Reducing maintenance costs
- Providing bonus goods after every nth production cycle
- Changing the type of workforce required by the building
- Increasing or decreasing the number of required modules or farm fields for a building
- Providing a certain type of fertility to farm buildings within radius, allowing goods to be produced on an island even if that island does not have the fertility 
Most items only apply to certain types of buildings, which are listed on the tooltip for the item.
Most item effects are additive; Having two items slotted that both apply a +25% production effect would provide +50% bonus to production buildings within range (meaning that those production buildings would run at 150% speed if no other modifiers were active, running 1.5 times as fast, producing 1.5 times as many items and requiring 1.5 times as many resources, compared to a similar building that is not within range of the Trade Union).
As other circle-radius public buildings, Trade Unions support clipping.
List of items
The lists of items which can be equipped in Trade Unions can be seen on following pages:
- Trade Union items: common
- Trade Union items: uncommon
- Trade Union items: rare
- Trade Union items: epic
- Trade Union items: legendary
- When applied to a building that has modules or fields, the item's bonus effect is applied as long as the main production building is within range of the Trade Union (the fields themselves do not have to be in range).