Unions often oppose increases in the prices of complementary inputs (for example,truck drivers may oppose increases in taxes on diesel fuel) .They do this because increases in the prices of complementary inputs might:

A) increase the supply of competing labor through the output effect.
B) increase the supply of competing labor through the substitution effect.
C) decrease the demand for union labor through the output effect.
D) decrease the demand for union labor through the substitution effect.

Complementary Inputs

Goods or services that are used together in production, where an increase in the use of one leads to an increase in the effectiveness of the other.

Substitution Effect

(1) A change in the quantity demanded of a consumer good that results from a change in its relative expensiveness caused by a change in the good’s own price. (2) The reduction in the quantity demanded of the second of a pair of substitute resources that occurs when the price of the first resource falls and causes firms that employ both resources to switch to using more of the first resource (whose price has fallen) and less of the second resource (whose price has remained the same).