Safety inspections are being carried out between Carrbridge and Inverness with a number of ScotRail services disrupted.
The Perth to Inverness line has been closed with services between Glasgow Queen Street and Inverness revised as a result of the inspections.
ScotRail confirmed all stations between Perth and Inverness will not be served and a number of rail replacement buses were available.
Citylink ticket acceptance is now in place.
A number of staff absences due to illness also impacted services this morning with services between Inverness and Wick have pulled from the schedule after a member of on-train staff fell ill.
The 2pm Inverness to Wick services has been withdrawn.