Buses will replace trains for 11 days on a section of the route between Inverness and Aberdeen while work to enable a new station takes place.
ScotRail has urged customers to plan ahead while extensive work around the Inverness Airport Station takes place.
Services will be disrupted until early morning on Wednesday 26 October.
Passengers from Aberdeen and Inverness will see buses replace trains between Inverness and Nairn.
Buses will also replace trains between Elgin and Inverness, calling at Forres and Nairn.
The BBC says ScotRail has arranged for an early morning bus to depart from Elgin to Aberdeen at 04:13, calling at all stations.
At night, the 22.00 Aberdeen to Inverness train will terminate at Inverurie, with buses in place for travel between Inverurie and Inverness.
The new station will have a passing loop through the station, and enhance sections of track and signalling within the area.
David Simpson, ScotRail service delivery director, said: "We know lengthy line closures can be a real inconvenience for customers, and we're doing everything we can to keep people moving during the work."