  Extensions of the Standard Model are required to give mass to the light
neutrinos and explain neutrino oscillations. One of the simplest ideas is to
introduce new heavy, gauge singlet fermions that play the role of right-handed
neutrinos in a seesaw mechanism. They could have large Yukawa couplings to the
Higgs boson, affecting the production of the Higgs bosons in association with a
pair of W bosons at future lepton colliders. Working in the inverse seesaw
model and taking into account all possible experimental constraints, we find
that sizable deviations, as large as 66\% are possible. This makes the
$W^+_{}W^-_{}H$ production cross-section a new, promising observable to
constrain neutrino mass models. The effects are generic and expected to be
present in other low-scale seesaw models.
