The rail union RMT said a six inch gap had been found on the track at Hambleton South Junction, near Selby.
The union highlighted a similar problem last December at Colton junction, just a few miles away.
RMT says it is concerned that staffing cuts are putting passengers at risk of a potential accident – something that was last night denied by Network Rail which said safety was not being compromised.
Network Rail said a dip, found on January 17, was scheduled for repair on February 2, but the line deteriorated and it was done earlier than scheduled.
A spokeswoman for Network Rail said: “A dip in our track was identified and spotted at Hambleton on January 17.
“Following our well-tried and tested standard industry procedure to remedy such dips, we scheduled an intervention to repair this dip on the Saturday night of February 2.
“Unfortunately the track deteriorated more quickly than is to be expected and, on discovering the broken rail, all traffic was stopped immediately while a repair was carried out.”
She added: “This incident was managed within all safety standards and was in no way affected by changes to staffing levels. Safety issues will never be compromised in the name of managing costs.”
Yesterday, the RMT released a picture, which it said was taken on February 1, showing six inches of rail head crumbled away to nothing on the InterCity East Coast Mainline, at Hambleton South Junction, near Selby, where normal running speeds are 125mph.
The union raised concerns that the 6in gap could have derailed a train.
RMT General Secretary, Bob Crow, said last night: “This shocking new picture highlights the reality on Britain’s railways today – staffing, inspections and track renewals have been cut.
“If we don’t reverse the cuts on Britain’s railways another major tragedy is inevitable.”