The criteria, distinguishing reciprocal media from nonreciprocal media are well known. However, with the development of fiber ring interferometry, effects of phase nonreciprocity caused by polarization effects, have been found in media, which are reciprocal in the traditional meaning. The polarization effects occur when waves, which have been equally polarized at the input, become differently polarized after passing through a fiber ring interferometer in counter directions. There are some papers, which provide calculations and results of experiments on the effects of polarization nonreciprocity for concrete schemes. The aim of the present work is to summarize the known results, and to analyze the effects of polarization nonreciprocity based on the general Jones matrix of FRI, which satisfies the well- known criterion of reciprocity.