* A specific labor union: For example, "The United Auto Workers union is on strike."
* A union of states or countries: For example, "The European Union has 27 member states."
* A political or social union: For example, "The Soviet Union was a communist state."
You don't capitalize "union" when it's used as a general term, such as:
* "They formed a union to improve their working conditions."
* "The two countries are in a union."
* "The union of two elements creates a compound."
Here are some examples to illustrate:
Capitalized:
* "The United Auto Workers union is on strike."
* "The European Union is a major economic power."
* "The Soviet Union collapsed in 1991."
Not capitalized:
* "The workers decided to form a union."
* "The two countries are in a union to fight terrorism."
* "The union of hydrogen and oxygen creates water."
If you're unsure whether to capitalize "union," it's always best to err on the side of caution and capitalize it if there's a chance it refers to a specific entity.