Southern rail passengers have been warned that services will be "severely disrupted" over the next few days because of a fresh strike by guards and an ongoing overtime ban by drivers.
Members of the Rail, Maritime and Transport union will walk out for three days from New Year's Eve in a long-running row over the role of conductors, while Aslef is continuing with a ban on overtime in protest at driver-only trains.
The action will cause more travel chaos for passengers who have suffered delays and cancellations for months because of the industrial action, shortage of staff, sickness and other issues such as signalling problems.
Passengers are being advised to check before they travel over the New Year period.
Southern said it will have a team of "contingency conductors" keeping key routes open, but services on some routes will be reduced and finish earlier, while other routes will have no services or a replacement bus service.
Services on all routes will be subject to possible cancellation and severe disruption because of the on-going driver overtime ban.
Alex Foulds, Southern's deputy chief operating officer, said: "While we will do everything we can to get passengers where they want to go, we have to warn people that journeys may be disrupted and take longer than normal.
"Our best advice is to check on the day you travel, particularly if you are heading out to New Year celebrations, as services on some routes finish early in the evening.
"We are sorry that yet again passengers will have their plans disrupted by what is pointless industrial action. Our door remains open for meaningful talks and we urge the RMT to see sense and join us in delivering a better railway for everyone in 2017."
RMT leader Mick Cash said: "The solution to this continuing chaos is in the hands of Govia Thameslink Railway - which runs Southern - and the Government.
"If the owners, the Go Ahead Group, spent a fraction of the millions they are stockpiling in profits and dividends on staffing and safety this dispute could be resolved overnight. RMT remains available for talks."
On New Year's Eve there will be no Southern train services on these routes: Clapham Junction - Milton Keynes; Chichester - Portsmouth/Southampton; Lewes - Seaford; Eastbourne - Ashford International; Oxted - Uckfield; Haywards Heath - Lewes; Redhill - Reigate.
These routes will either have ticket acceptance with another operator or a replacement bus service.
On Sunday 1 January there will be a Sunday service and on Monday 2 January there will be a Saturday service.
On both 1 and 2 January there will be no Southern train services on these routes: Ashford - Hastings; Hurst Green - Uckfield; Havant - Portsmouth Harbour; Clapham Junction - Milton Keynes; Redhill – Reigate.
These routes will either have ticket acceptance with another operator or a replacement bus service.
On 2 January there will also be a significantly reduced service from Brighton for stations towards Hove, Littlehampton and Havant and Southampton. Services that would have run from London or Brighton to Portsmouth will run only to or from Chichester.