Passengers will face rail chaos over Christmas, unless a deal to avoid further strikes can be struck by Monday, according to a leaked industry document.
A private briefing from Network Rail shows the publicly-owned rail track operator is preparing for up to 26 days of disruption across the country between December 13 and January 6.
Over 40,000 RMT members across Network Rail and 14 rail firms will take walk out for eight separate days over the Christmas period - on top of an overtime ban lasting from 18 December until 2 January which will further hit services.
It comes as transport union TSSA ramps up industrial action on railways during December.
TSSA has announced fresh strike action across Network Rail and a dozen train operating companies over Christmas, including GWR and Avanti West Coast.
Thousands of their members are taking action short of a a strike from 13 December until early January.
Rail bosses suggest the strikes must be called off by Monday as emergency rotas and agreements with the train companies will be locked in after that point.
The leaked document said: "The industrial action announced by the RMT this week is the biggest single piece of industrial action the rail industry has ever seen. In all there could be 26 days of disruption to the rail network from 13 December through to 6 January.”
It adds: “In order to reset and run a full service over the Christmas period, in addition to our vital engineering works, industrial action must be called off by 5 December.”
The strikes are set to go ahead, despite Network Rail telling its managers they have reached an agreement with unions over changes to sick pay.
An RMT spokesperson denied this, telling the Mirror: "Nothing has been agreed and negotiations are ongoing."
But RMT leader Mick Lynch has demanded that Transport Secretary Mark Harper “unshackles” the train firms to allow them to offer pay hikes.
Mr Harper has now stepped into negotiations as a “facilitator” and is holding weekly meetings with rail firms and unions in an effort to reach a deal.
Unions have already come to agreement with publicly-owned Transport for Wales, ScotRail and London Underground over pay.
Network Rail added in the leaked doc to managers: “We remain committed to resolution. However, we are also working hard now to prepare for the industrial action announced by the RMT.”
A Network Rail spokesperson said: “We currently have a number of policies regarding sick leave and absenteeism and are working with the unions to standardise and simplify the process across the network.
"Discussions with the unions are ongoing and good progress has been made.“
