A new method is suggested for finding the reflection and transmission amplitudes of an arbitrarily polarized electromagnetic plane wave incident on a one-dimensional finite size dielectric medium. Within the transfer matrix method it is shown that the problem reduces to a set of first-order differential equations with the scattering amplitudes being functions of the size of the medium. We also show that when the unknown functions are chosen as a suitable combination of a scattering amplitudes, the problem reduces to a Cauchy problem for the wave equations describing the s- and p-polarized waves.