we well visit Paris in June, traveling in the morning on 17th June from a hotel near CDG (at Parc des Expositions) to the Eiffel Tower and in the evening from Paris to Disneyland to an other hotel. Our plan was to buy Mobilis for us and Youth Weekend daypass for the children and use RER B, metros and RER A to move around on Sunday.
Now that day is a planned SNCF stirke day. We have one scheduled program: we have booked tickets for Eiffel Tower at 12:00. Other programs are flexible. So my concern is whether we can make it in the morning with RER B and metro or RER C to Eiffel Tower.
My questions are: how crowded are RER B trains heading to city center on a normal Sunday morning? Can we expect that half of the trains will be running? Is it OK to take the train at Parc des Expositions or is it better to go back to CDG? Should we look better into alternatives (bus, taxi)?
During Paris train strike action, RER B will be likely running at 1/2 frequency. Without luggage on a Sunday morning I would think it would be quite manageable to take the RER B even with strike action taking place. Just give yourself an extra 30 minutes and you should be fine. Paris Metro will be unaffected by strike action (it's not of SNCF's concern) and the RER A is only affected on a particular leg which is not the Disneyland / Marne La Vallee leg of the RER A train route.
There aren't a lot of bus options from Parc des Expositions into central Paris other than the airport buses which require special fares not covered by Mobilis / Ticket Jeunes.
In the case that you do need taxi service, be aware that Uber operates in Paris so it may be easier to hail / direct than a normal cab (prices are roughly the same).