As part of the ongoing industrial action (which is set to run for another month at least), the French rail network SNCF will be on strike on May 28 and 29 next (2018). In real terms, this means that although trains actually run it is notoriously difficult to know in advance which ones will run. The recent strike actions have only been followed by about 15% of the workforce. But that is more than enough to seriously disrupt the services.
As for previous strikes, it is advisable to make other plans if you have fixed appointments. That involves either leaving far earlier or using the car-pooling services.