The largest union at Samsung Electronics Co. went on a strike for the first time in the company’s 55-year history, with the standoff over pay so entrenched that the two sides have stopped all discussions. The National Samsung Electronics Union, the largest of the tech giant’s several unions with some 28,400 workers, encouraged members to take a single day off on Friday, which falls between a Thursday public holiday and the weekend. They plan to resume normal work hours next week....