"Unprecedented" sickness levels and drivers taking annual leave are expected to lead to Northern rail cancellations on Christmas Eve.
A spokesman said the cancellations would be "pre-planned" but did not specify which routes would be affected nor the number of services cut.
The warning comes after commuters were
hit by delays and cancellations as new winter timetables were launched.
The spokesman advised people to check online before travelling.
"Alongside the annual leave entitlements at this time of the year, we currently have unprecedented levels of sickness," he said.
"That means we expect there to be some pre-planned cancellations on certain lines.
"We are sorry for any disruption customers may face."
Image copyrightTIM NASH
Image captionNorthern has received widespread criticism for repeated cancellations and delays
The Department for Transport (DfT) reiterated its position on the future of the rail firm, which has received widespread criticism for regular disruption to services.
A DfT spokesperson said: "As the Secretary of State for Transport, Grant Shapps announced at the Transport Select Committee in October, we are developing contingency plans for the replacement of the current franchise with either a new short-term management contract with Northern or the Operator of Last Resort."
David Brown, managing director at Northern, said the franchise had faced "unprecedented challenges" outside its control.
He said the late delivery of major infrastructure upgrades, strike action and lower than expected economic growth have had "a significant effect" on the business plan agreed with government in 2015 but Northern and parent company Arriva "remain fully committed to delivering the transformation of the north's railways and improving customers' experience".
A £600 million investment would see 2,000 extra services per week, better stations and better offers for customers, he said.
The Metro Mayors of Liverpool and Greater Manchester called on the government to make clear what could happen to Northern following reports it would be stripped of its franchise.
Steve Rotheram, Metro Mayor of Liverpool City Region, said there needed to be "some consequence" for the "very, very poor service" and "chaos" rail passengers have faced on the network.