Just one in five commuter rail trains are running on some lines in Paris on Tuesday due to a strike over bonus pay for staff.
For other lines, the service is less severely impacted, but many are only running during peak hours.
The Transilien Paris regional network, a branch of France's national railway company, has encouraged people to work from home or to find alternate transport for the working day, which follows Monday's bank holiday.
The SNCF is meeting with unions on Wednesday to try to reach an agreement.
Train drivers are calling for bonus payments for working through the Olympic period when more than 15 million tourists to Paris are expected.
"We thought the talks were dragging on a bit and wanted to provoke something," Fabien Villedieu of the SUD-Rail union told Agence France-Presse last Friday.
"We have a heavy workload with 4,500 additional trains in August, so a whole range of our colleagues won't be able to go on holiday," he added.
Staff employed in other public sector services, such as hospital workers, have also threatened to strike during the Olympics.
Paris' rubbish collectors last week won a pay rise as well as an Olympic bonus, subsequently retracting the threat of summer strikes.
Metro and bus operator RATP has already offered an average bonus of €1,000 to workers, and this can reach up to €2,500 euros for the most sought-after drivers.
France's interior ministry, meanwhile, has offered police officers bonuses of up to €1,900 to work during the Olympics.
