Optical absorption bands below the band gap in n-type Sic are discussed in the framework of first-principles band structure calculations. While the peak positions and their polarization are well reproduced in a pure band-to-band model, the widths of the spectra obtained for samples with high impurity concentrations indicate a significant role of the band tailing due to the N-impurities. This leads to a partial breakdown of the vertical selection rule, which we take into account by means of a density of states calculation over a limited region of k-space, and a weaker breakdown of symmetry selection rules. Differences for samples with low concentration of dopants and the possibility of impurity resonances in the continuum are discussed.