In economics, the lump of labour fallacy is the misconception that there is a fixed amount of work—a lump of labour—to be done within an economy which can be distributed to create more or fewer jobs. It was considered a fallacy in 1891 by economist David Frederick Schloss, who held that the amount of work is not fixed.

The term originated to rebut the idea that reducing the number of hours employees are allowed to labour during the working day would lead to a reduction in unemployment. The term is also commonly used to describe the belief that increasing labour productivity, immigration, or automation causes an increase in unemployment. Whereas opponents of immigration argue that immigrants displace a country's workers, this is a fallacy, as the number of jobs in the economy is not fixed and immigration increases the size of the economy and may increase productivity, innovation, and overall economic activity, as well as reduce incentives for off-shoring and business closures, thus creating more jobs.

The lump of labor fallacy is also known as the lump of jobs fallacy, fallacy of labour scarcity, fixed pie fallacy, and the zero-sum fallacy—due to its ties to zero-sum games. The term "fixed pie fallacy" is also used more generally to refer to the idea that there is a fixed amount of wealth in the world. This and other zero-sum fallacies can be caused by zero-sum bias.