A critical round of contract talks between...

A critical round of contract talks between Eastern Airlines and its Machinists union could collapse early this week after the abrupt departure of the union’s chief negotiator, officials involved in the talks said. Bill Sheri, who acted as union spokesman in sessions Friday and Saturday in Key Largo, Fla., left the talks without explanation Sunday. Further negotiations were scheduled for today, but sources said Eastern may drop out of the talks early this week if they are not satisfied with the union’s explanation for Sheri’s hasty departure.