Passengers were warned not to travel on a busy rail route today because of a lack of available train drivers.
First Capital Connect (FCC) said there will be no service on its Great Northern route, and trains it does operate are likely to be "extremely busy".
Union leaders said workers were not taking industrial action but were merely exercising their contractual right not to work on Sundays.
London Midland services were disrupted in the summer in a similar case.
FCC said it strongly advised against rail travel unless absolutely necessary, adding that, if journeys were essential, tickets would be accepted on alternative bus and rail routes in areas including London's Liverpool Street and King's Cross stations, King's Lynn, Cambridge, Huntingdon, Bedford, Hitchin, Stevenage, Luton Airport and Peterborough.
FCC said in a statement: "We are continuing to work towards a resolution to these problems and to provide alternative transport where possible and will post any updates on our website.
"We regret any inconvenience this disruption will cause."
FCC, which employs around 600 drivers, said it was disappointed that there would be hardly any Great Northern trains on Remembrance Sunday, and it has been contacting local officials of the Royal British Legion to warn them of the problem.
FCC is currently involved in pay talks with unions.
It is believed that drivers have been refusing to work overtime and rest days for the past two weeks, leading to cancellations and delays.