In the framework of the QCD effective action the vertices of gluon emission in interaction of reggeons are studied in the limit of small longitudinal momenta of the emitted gluon. It is found that the vertices drastically simplify in this limit, so that the gluon becomes emitted from a single reggeon coupled to the projectile and target via multireggeon vertices. The contribution from this kinematical region is studied for double and 2 × 2 elementary collisions inside the composite projectile and target.