Answer:
When labor unions successfully bargain for wage rates that are HIGHER THAN the equilibrium wage rate, they may cause AN INCREASE IN STRUCTURAL UNEMPLOYMENT.
Explanation:
When a labor union bargains for wages that are above equilibrium rate, this will produce the same effect as a price floor. The supply of labor will increase, while the demand for labor will decrease. This deadweight loss generated by high wages will result in an excess supply that will eventually lead to higher structural unemployment.