  We argue that future e^{+} e^{-} linear colliders can produce many sneutrinos
if lepton-number violating couplings lambda_{1j1} exist and enough beam
polarization is obtained. The terms lambda_{ijk} L_{i} L_{j} E_{k}^{c} are
allowed in a discrete Z_{3}-symmetry which is used to forbid rapid proton
decay, and it is worthwhile to consider the possibility of the existence of
such terms and their resultant. We study the process e^{+}e^{-} -> sneutrino ->
e^{+} e^{-} in detail, and show that if such resonance is not found,
lepton-number violating couplings lambda_{1j1}, will be strongly constrained.
If we assume sneutrino mass m_{sneutrino}=500 GeV, beam polarization
P_{e^{-}}=0.9, P_{e^{+}}=0.6, and integrated luminosity L=100 fb^{-1},
non-observation of sneutrino resonance will lead to lambda_{1j1} < 0.02 (if all
charginos, and neutralinos, are lighter than the sneutrino), or lambda_{1j1} <
0.003 (if all charginos, and neutrainos, are heavier than the sneutrino).
