Several train services have been cancelled following the theft of signalling cables near Lancaster overnight.
Transpennine Express has warned rail users to expect disruption on between Preston and Carlisle as fewer trains will be able to run on these lines and services may be suspended.
Train services between Lancaster and Morecambe will also be cancelled on Monday morning and a bus replacement service is expected to operate, says Northern.
Lancaster and Barrow-In-Furness trains may be delayed by up to 10 minutes and may terminate at Carnforth.
A spokesman for the Northern said in a statement: "Due to theft of signalling cables at Lancaster some lines are blocked. Disruption is expected until around midday on Monday.
"If you've been delayed by 30 minutes or more, hold on to your tickets and claim compensation."
Travellers are advised to check before they travel here.
Virgin West Coast has advised its services will be operating at a reduced speed through the Lancaster and Lake District Area.