I had a similar situation last November, when an over-eager Lufthansa check-in officer denied boarding the plane because I was using a Finnish national ID card.

I had a similar situation last November, when an over-eager Lufthansa check-in officer denied boarding the plane because I was using a Finnish national ID card. I was travelling from Finland to Croatia and the explanation was that Croatia had enabled passport checks on border and ID card is no passport. No amount of explanation helped. I did have my passport with me and I showed it to this lady. Rest of the trip I used only the ID card. Common theme seems to be, at least in Finland, that dealing with public agencies and authorities is just fine, but you can get to a trouble with private companies.