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Detailed calculations are carried out for the electron-impact excitation cross sections from the ground state to the individual magnetic sublevels of the 1s2s22p3/2J =2 excited state of highly-charged beryllium-like ions by using a fully relativistic distorted-wave (RDW) method.The contributions of the Breit interaction to the linear polarization of the 1 s2s2 2p3/2 J =2 → 1 s22s2 J =0 magnetic q uadrupole (M2) line are investigated systematically for the beryllium isoelectronic sequence with 42 ≤ Z ≤ 92.It is found that the Breit interaction depolarizes significantly the linear polarization of the M2 fluorescence radiation and that these depolarization effects increase as the incident electron energy and/or the atomic number is enlarged.