The influence of the inner-shell electron dynamics of an atomic system on its non-linear characteristics in a field of laser radiation is studied theoretically. The quasienergy approach is developed to take into account the correlation interaction. We use the random phase approximation, in which the correlation effects are accounted for by considering the time-dependent interaction potential of a photoelectron with oscillations of the electron density of the inner electrons. In the following calculations the polarisational approximation for this potential was used. Explicit calculations in the case of linear polarisation of the laser field are made for negative ions of halogens and alkaline atoms in the central field approximation both with and without account taken of the inner electron dynamics. The results show that there is substantial suppression of non-linear characteristics when one takes the correlation interaction into account. This is in agreement with the results of several other studies.