A railway worker has died in an accident near Sleaford railway station.
It is understood he died on Friday while carrying out routine maintenance on the track.
Investigators have said the man suffered a heart attack after jumping out of the path of an oncoming rail trailer.
British Transport Police and the Health and Safety Executive have launched an investigation and were meeting to discuss the accident.
He was employed by contracting firm Mowlem, which has said it is helping with the investigation.
The repairs at the site are part of an ongoing programme of improvement on the line which runs between Grantham and Skegness.
Bob Crow, general secretary of the Rail Maritime and Transport union said: "We are reiterating our demand for a public inquiry into the safety regime of the fragmented privatised rail industry."
The accident comes less than a month after four workers were killed by a runaway wagon on the West Coast Main Line in Cumbria.