The high luminosity projects imply collisions of intense short bunches with micro‐beta at the IP, which entails high variations of the particle energy on the IP passage, due to the opposing bunch electric fields. This effect is shown to put the limit on the attainable luminosities. The estimates are made for the stability of the incoherent and coherent longitudinal motion which enhance the required RF voltage depending on the design beta minimum at the IP. The results of the analytical treatment and the computer simulation of the off‐axis particle synchrobetatron motion relate the limitations, imposed on the space charge parameter by the longitudinal beam‐beam effects, and the main parameters of the machine.