trades unions

Noun

 * 1)  when referring to unions representing different trades.
 * 1)  when referring to unions representing different trades.

Usage notes
Some authorities, chiefly in the UK, suggest that the plural of trade union is when the relevant unions all represent the same trade (for example, "The train drivers were divided between two trade unions."), but  when they represent different trades (for example, "There are hundreds of trades unions in England."). However, is commonly used for both cases.