The strike, starting on Monday evening and due to run for three months in successive waves of two days, is set to be a major test of President Emmanuel Macron's ability to push through reforms, Reuters reported.
It is also a test for unions, which have struggled so far to mount a united front to seriously challenge Macron's push to reform the economy and the labor market.
Some 53 percent of the nearly 1,000 people surveyed on March 30-31 considered the rail strike was not justified, down from 58 percent two weeks earlier, the Ifop poll for Le Journal du Dimanche newspaper found.
The four main unions representing rail workers have called the two-day strikes every three days for the next three months to protest against opening the national SNCF rail monopoly up to competition as required by EU law.
They fear employees could lose job-for-life guarantees, automatic annual pay rises and generous early retirement under the reform of the highly indebted SNCF.
"This strike is going to hit customers hard. It is designed to have a maximum impact on traffic," the state-appointed head of SNCF, Guillaume Pepy, told Le Journal du Dimanche.
Transport Minister Elizabeth Borne has promised a gradual opening of the rail network to competition from 2020 and has offered assurances that existing rail workers would have to make few sacrifices.
"Current rail workers will keep their (employment) status and most of their advantages if they are moved to a competitor. In these conditions, I've got to ask what's the problem?" Borne told Le Parisien newspaper.
A reform of the labor code in September left unions divided with the biggest, the CFDT, opting out of strikes organized by the second-biggest, the CGT.