Oooh, come oooooon... There probably hasn't ever been a single year _without_ something resembling a "massive strike" in France. And we have yet-another-pension-reform coming up.
It's like predicting there will be a massive barbecue in Texas :P
Burned vehicles, a few hands lost to a police grenade, maybe a death or two.
Sure it's a low hanging fruit, but the French executive power has been bypassing parliament with 49.3 rulings for the past year to get unpopular laws and welfare undoings through. Something's gotta break.
And even if they did not have to bypass parliament, there would be strike (source : the last 50 years or so ?)
Can't really remember one for this year. Then again, there are still five more days to.
One not massive in numbers, but massive as impact was concerned: oil refineries, only 2 months ago.
It impacted the whole country for weeks. As the Gilets Jaunes happening didn't even involve any strike, I guess this one qualifies even better.