The start of a harmful development
--Identity cards for football supporters could be the thin end of the wedge - soon everyone might have to carry identification.
I'm sure I have seen an entry on Lexilogia which matches this idiom exactly but I cannot for the life of me find it! :twit:
However, I'm not sure that the proposed translation in proz could be used in the case of your example, as this one shows fear for something that could be in the making, not of something existing (just not visible).
I think, in the case of your example, it would be better to leave icebergs aside and try for other phrases, starting with [...] μπορεί να είναι μόνο η αρχή. Another idea is άρχισαν τα όργανα, e.g. Με τις ταυτότητες για τους φιλάθλους άρχισαν τα όργανα... (musical instruments, that is).