We study the in-plane electronic anisotropy in the parent compounds of several families of Fe-based superconductors (BaFe2As2, EuFe2As2, NaFeAs, LiFeAs, FeSe, and LaFeAsO) by polarization-resolved Raman scattering. We measure intensity of the fully symmetric c-axis vibration of As atom mode in the XY scattering geometry and notice that the mode's intensity is significantly enhanced below the magnetostructural transition only for compounds showing magnetic ordering. In particular, we find that the intensity ratio of this As phonon in the XY vs. XX scattering geometries is proportional to the square of the ordered magnetic moment. We relate this As phonon intensity enhancement below the Néel temperature in iron pnictides to in-plane electronic anisotropy induced by the collinear spin-density wave order.