  We study the effects of new dimension--6 operators, resulting from a general
$SU(3)_C \otimes SU(2)_L \otimes U(1)_Y$ invariant effective Lagrangian, on
three jet production at LEP and at the Next Linear Collider. Contributions to
the total event rate and to some event shape variables are analysed in order to
establish bounds on these operators.
