Do trade unions raise wages?

Critics argue a union raises pay by cutting the number of jobs

A union is the sole seller of its members' labour, so it can act like a monopoly: by threatening a strike, it can win a wage above the market equilibrium. At that wage firms hire fewer workers than they otherwise would, often by not replacing leavers rather than by sacking anyone, and more people want union jobs than there are posts. Critics say unions grab as much as they can in the short term, even when it injures workers in the long run.