The National Transportation Safety Board (NTSB) will be investigating the deaths of two San Francisco area transit workers who were killed on Saturday when they were struck by a commuter train.

The fatalities came amid a strike by employees of the Bay Area Rapid Transit (BART) system. A statement by BART said the train was being run in automatic mode under computer control at the time of the accident, and that an “experienced operator” was at the controls.

The NTSB says its investigators will be on the scene for several days gathering information.

The victims were a BART employee and a contractor who were performing track inspections in response to a reported dip in the track, BART said. The accident occurred northeast of San Francisco in Walnut Creek, California.

Workers walked off the job after contract negotiations between BART management and unions leadership came to an impasse on Thursday.

Union officials had warned that allowing managers to operator trains during the work stoppage could be dangerous.

AFSCME 3993 President Patricia Schuchardt, said in a statement. "Our hearts go out to the family of both workers as well as to the person operating the train. This is a tragedy."