Unions, including those representing air traffic controllers and rail signalling workers, are protesting president Emmanuel Macron’s introduction of a new universal pension scheme.
The country’s rail network, SNCF, has announced only one-third of Transilien suburban services will be running, the metro is operating a reduced service, and Eurostar will be affected.
Euronews has reported there will be action in Lyon, Toulouse, Bordeaux, Lille and Rennes alongside the main action in Paris.
The Eiffel Tower has been closed for the day in light of the rallies, and there are already mobilisation calls for 11 January.
The French strikes have now been ongoing for 36 days.
An easyJet statement said the strikes started at 6pm on 8 January and will continue until 5.30am on 10 January.
"We expect there will be delays and cancellations due to the industrial action, therefore we advise all customers to check the status of their flight on our flight tracker," it said.
The Foreign and Commonwealth Office (FCO) has also changed its advice.
"On Thursday 9 January and Saturday 11 January there will be a further call by unions for widespread industrial action and demonstrations across France, including to transport," it said.
"If you’re due to travel on these days, check with your travel operator for further information. Avoid demonstrations wherever possible and follow the advice of the local authorities."
