The Laborers' International Union of North America, Local 578, and Shaw Stone & Webster Construction, Inc., agreed on a provision in their collective bargaining agreement that required all employees to pay dues to the union. Sebedeo Lopez went to work for Shaw Stone without paying the union dues. When the union pressed the company to -re him, Lopez agreed to pay. The union continued to demand his discharge, however, and Shaw Stone -red him. Was the union guilty of unfair labor practices? Why or why not?