Services in the Paris suburbs, the northeastern Champagne-Ardenne region and the southern Occitanie region, which includes Toulouse and Montpellier, were particularly affected.
The industrial action began on Friday after a train in north-east France slammed into a truck at a level crossing, leaving 11 people injured.
The train driver was himself among those hurt but being the sole employee of state railways company SNCF on board had to help take care of passengers.
Unions said the incident highlighted what they say is a problem of understaffing on trains, notably the absence of ticket inspectors on some lines.
- All France's OUIGO trains cancelled on Saturday due to strike
- Trains across France delayed and cancelled due to unexpected strike
Since Friday, staff have been exercising their “right to withdraw” their labour — a clause that allows workers to walk off the job in case of “clear and present danger to their life or health.”
SNCF's management has accused the workers of abusing that right to indulge in a wildcat strike on a busy weekend for train travel, at the start of the mid-autumn school holidays.
It argues that some train lines have not had ticket inspectors for decades.