  We discuss the occurrence and the stability of charge density plateaux in
ladder-like $t-J$ systems (at zero magnetization M=0) for the cases of 2- and
3-leg ladders. Starting from isolated rungs at zero leg coupling, we study the
behaviour of plateaux-related phase transitions by means of first order
perturbation theory and compare our results with Lanczos diagonalizations for
$t-J$ ladders ($N=2\times 8$) with increasing leg couplings. Furthermore we
discuss the regimes of rung and leg couplings that should be favoured for the
appearance of the charge density plateaux.
