The rail operator has already blocked anyone from booking tickets for December 5th to December 9th on some lines, and today some passengers who have pre-booked tickets reported getting emails and text messages telling them their train is cancelled.
The early cancellations represent an unusual move from SNCF, which has said it will not be publishing its full strike timetable until December 3rd.
Generally when there is a strike transport companies are told a few days in advance exactly how many employees will be walking out, and they then publish revised timetables based on their available staffing levels.
But in a sign of how disruptive the December action is expected to be, SNCF and Eurostar are cancelling services and suspending bookings a week in advance.
Around 150,000 customers of SNCF received a message saying their train was déjà supprimé (already cancelled) and inviting them to either exchange the ticket for a different time or receive a full refund.
The Eurostar service has already announced the cancellation of 25 trains over December 5th and 6th.
SNCF, Eurostar, Lyria and Thalys (who run the international train routes) are all offering customers free exchanges or refunds if they decide not to travel during the strike period.
The unions that cover the rail industry have declared an 'unlimited' strike, starting on December 5th.
How long the action is likely to last for his difficult to say, but one political analyst that The Local spoke to said it could last until the New Year.
As well as rail staff, unions representing Metro and bus drivers, airline ground crew and air traffic controllers, hauliers, lawyers, teachers, civil servants and postal workers have all said they will strike as unions prepare for a major confrontation with Emmanuel Macron's government over plans to reform France's pension system.
READ ALSO 'Strikes are the only way to get social progress in France' – unions justify December strikes