The government is concerned that Christmas train services could be disrupted by staff shortages, the rail minister has said.
Lord Hendy said that the transport department was going to "keep a close watch on staffing" throughout the holidays.
Disruptions may also be exacerbated by fresh industrial action, with Avanti West Coast train managers voting to strike for three days over the festive period.
Recruitment has proven difficult across the rail industry, leaving train operating companies dependent on staff volunteering to work extra paid shifts, particularly during big occasions.
A Department for Transport official told MPs that the railway system was generally "over-reliant on overtime working" for train crew, particularly around Christmas.
Many train drivers and other crew members do not have Sunday working included in their contracts, with some operators offering extra paid shifts to ensure services can run.
On Tuesday, the Rail, Maritime and Transport (RMT) union said that walkouts have been scheduled for 22, 23 and 29 December for Avanti services, after it rejected the train company's proposals for "rest day working arrangements".
Train managers typically work a 41-hour week but due to staff shortages can be asked to work on their days off.
The RMT has, however, described that the current arrangements as "unacceptable", with some 300 train managers expected to walk out.
Avanti West Coast said customers would face "significant disruption" during "our busiest and most important" time of the year.
It was announced weeks after RMT members working at a number of other rail companies accepted a pay rise of 4.75% for the last financial year, and a 4.5% increase for 2024-25.
Those working for Northern, however, recently rejected the firm's enhanced four-month pay offer for conductors working on Sundays.
As a result, passengers may see disruption across its services in December, the company said.
Lord Hendy told MPs on the Commons Transport Committee that there were worries that closures of parts of the railway over Christmas may put more pressure on others.
Britain's rail network completely shuts down every year on Christmas Day, with a limited service on Boxing Day.
Many routes will be closed for longer during the festive period because Network Rail, which owns and maintains the railways, will be carrying out engineering work.
Lord Hendy, who chaired Network Rail from 2015 until he was brought into the Labour government, said: "Christmas is a good time to do major engineering work, because the demand is lower over several days."
Network Rail has previously said passenger numbers at major stations typically drop by 50 to 60% during the seven days between Christmas Day and a new year compared with a week in November or early December.
- London Liverpool Street station will be closed from Christmas Day until 2 January. Travellers are advised to use Victoria line Tube services from Walthamstow Central or Seven Sisters.
- No trains will call at London Paddington between 27 December and 29 because of preparatory work necessary for HS2's Old Oak Common station.
- Heathrow Express trains will be unable to run between Paddington and the west London airport.
- Some Great Western Railway services will be diverted to or from Euston, but the majority will stop or start at Reading or Ealing Broadway.
- Signalling work in the Crewe area between Christmas Day and January 2 will cause significant changes to services, with no trains passing through Crewe station on 27 December.
- There will be no direct services between Crewe and Liverpool, and a reduced service between Crewe and Manchester, from 28 December until 3 January.
- Services in the Cambridge area will be disrupted between 27 December and 5 January, affecting CrossCountry, Greater Anglia, Great Northern and Thameslink services.