A more thorough explanation:

Definition: Black-leg labor is a term used to describe a worker who works under conditions that go against a union contract. This can include a worker who crosses a union picket line to replace a union worker during a strike. In British English, black-leg labor is another term for a strikebreaker.

• During the strike, the company hired black-leg labor to keep the factory running.
• The union members were angry when they saw the black-leg workers crossing the picket line.
• Some people believe that black-leg labor is necessary to keep the economy running smoothly.

These examples illustrate how black-leg labor is used to describe workers who go against the union's wishes during a strike. In the first example, the company hires black-leg labor to keep the factory running despite the strike. In the second example, the union members are upset when they see black-leg workers crossing the picket line. In the third example, some people argue that black-leg labor is necessary to keep the economy running smoothly, even if it means going against the union's wishes.