  It is shown that layered superconductors are subjected to a phase transition
at zero temperature provided the order parameter (OP) reverses its sign on the
Fermi-surface but its angular average is finite. The transition is regulated by
an elastic impurity scattering rate $1/\tau$. The excitation energy spectrum,
being gapless at the low level of scattering, develops a gap as soon as the
scattering rate exceeds some critical value of $1/\tau_\star$.
