The actual filings before FISA are secret; they're signals intelligence cases. The laws the FISA court uses to authorize surveillance are not secret.
Source: https://www.eff.org/deeplinks/2013/06/government-says-secret...
Well, so far as we know anyway. There is still, AFAIK, an open question about the existence and/or exact nature of "secret laws" in the US. See John Gilmore's struggle to travel without offering up identity documents[1], for example.
But the prevailing view seems to be that the whole FISA program is a system of secret laws, which is not in fact the truth.