Just a guess, but I'd have thought it's more likely to be the flu than any sort of FCC▸ -related industrial action (which would be unofficial anyway). I'm not sure if what's happening at FCC even technically counts as industrial action, since all they're doing at the moment is exercising their contractual right not to make themselves available for duty on a Sunday.
I call a spade, a spade. As far as I'm concerned, working to rule
is industrial action. No doubt there was union organisation behind the FCC action - no way did all the drivers decide, independently, not to show up on Sunday. It is actually quite a powerful weapon that
ASLEF» can use. There is no need for a democratic ballot, with the necessary advance notification that this requires. One wonders in instances like this how many drivers felt pressured into not working their lucrative Sunday turn, lest they go against what the shop-stewards have unilaterally decided.
Also what happens to non-driving staff? Are they hit financially by losing a lucrative Sunday turn, or are they required to sign-in and sit in the staff-room all day twiddling their thumbs to earn that day's pay?