This afternoon I got confirmation from a member of CSA check-in staff that instructions were issued to Ruzyne CSA staff as well as to stations abroad that card use is to be very strictly checked.

That has a.o. the following consequences

a. in Ruzyne you will have to possibly show your card twice, once at check-in, and once at the boarding desk (where the upgraded boarding passes are issued). That happened to me on PRG-IST.

b. in Amsterdam you cannot use self check-in facilities - it issues a paper request to go to a check-in counter. The assistant will then ask you for your OK Plus card. You can, however, print the boarding pass yourself at home or hotel and bypass check-in if you are flying without checked luggage - requests for upgrades anyhow are dealt with at boarding, not at check-in.

I wonder what type of fraud it is they want to overcome.

Maybe it works -it was very quiet this week in C class on AMS-PRG (twice) and PRG-IST. IST-AMS was on KLM - they didn't care about the OK Plus card (maybe because I was flying paid C and that would anyhow ascertain lounge access).