  We study the Lepton number violating like-sign dilepton processes $h_1 h_2
\to l^\pm l^{\prime \pm} jj X$ and $h_1 h_2 \to l^\pm l^{\prime \pm} W^\pm X$,
mediated by heavy GeV scale Majorana neutrinos. We focus on the resonantly
enhanced contributions with a nearly on-mass-shell Majorana neutrino in the
s-channel. We study the constraints on like-sign dilepton production at the
Tevatron and the LHC on the basis of the existing experimental limits on the
masses of heavy neutrinos and their mixings $U_{\alpha N}$ with $\alpha =
\nu_{e}, \nu_{\mu}, \nu_{\tau}$. Special attention is paid to the constraints
from neutrinoless double beta decay. We note that searches for like-sign
$e^{\pm} e^{\pm}$ events at Tevatron and LHC may shed light on CP-violation in
neutrino sector. We also discuss the conditions under which it is possible to
extract individual constraints on the mixing matrix elements in a model
independent way.
