Complex sentence: That same year, a labor contract negotiation turned sour, leading to a prolonged work stoppage by non-operating unions beginning January 23,1963, and whose picket lines were honored by the operating unions (the train crews).
Split into simpler sentences: That same year, a labor contract negotiation turned sour. This led to a prolonged work stoppage by non-operating unions beginning January 23,1963, and whose picket lines were honored by the operating unions (the train crews).