A mu(+)mu(-) collider is an appealing machine to probe resonant CP-vio
lating transitions of a CP-even Higgs particle into the Z boson or int
o another CP-odd Higgs scalar. These phenomena are studied within a ma
nifestly gauge-invariant approach implemented by the pinch technique.
The CP invariance of an extended Higgs sector motivated by supersymmet
ric E(6) models is assumed to be broken radiatively by the presence of
heavy Majorana fermions. CP violation originating from Higgs-Z mixing
is found to be very modest, whereas CP-number-violating transitions i
nvolving Higgs scalars only can be resonantly enhanced up to order of
unity.