From the email:
In those circumstances, you would:
Lose staff travel permanently
Lose pay for any duties you miss if you go on strike, including associated days off
We would also need to review all costs in IFCE, including hotels. And of course I would be unable to maintain the assurances for your terms and conditions.
History tells us that absence rises significantly during industrial action. We will assume that anyone who does not report for duty during a strike is taking part in that industrial action.
Anyone out there still with any doubts?
Edit: Crossed posts with moo, who has posted the entire mail, so hopefully that's the last of the doubters convinced.