This paper studies effects of an electric field on the mechanical response of unidirectional carbon fiber polymer matrix composites. The existing experimental evidence suggests that exposure of a composite material to the electromagnetic field leads to changes in the material's strength and resistance to delamination. We have analyzed the effects promoting this phenomenon: coupling of mechanical and electromagnetic fields and Joule heat effects and develop an experimental setup for impact tests of the composites carrying an electric current. Experimental results of low velocity impact tests on unidirectional carbon fiber polymer composite plates carrying a DC electric current show that electrified composites fail at higher impact load. Moreover, a larger electric field leads to a larger impact load that may be sustained by the composite. Finally, analysis of the Joule heat effects reveals that it is not a primary mechanism for the strengthening phenomenon observed in the experiments.