(Providence, RI) -- It's the final day before a scheduled school bus drivers' strike that will affect Providence public school students. With retirement benefits at the center of a contract dispute, Teamsters Local 251, the union representing the drivers, sent a letter to union members yesterday disputing bus company First Student's claim that the union's pension fund is in distress. First Student says it cannot participate in a pension that is underfunded by more than three-and-a-half-billion dollars and lost seven-hundred-million last year. The union claims the pension fund is healthy and is improving.