Transition metal oxynitrides with the perovskite structure type are an emerging class of functional materials with a variety of interesting optical, photocatalytic, dielectric and magnetoresistive properties that may depend upon anion order. However, the oxide/nitride ordering principles in such materials were unclear until a recent study of the representative compounds SrMO2N (M = Nb, Ta) by neutron and electron diffraction revealed a robust partial anion order. The same order has since been confirmed in NdVO2N, and in LaTaON2 with O/N interchanged. A high resolution study is requested here to discover whether BaTaO2N has this local order of cis-anion chains in two or in three dimensions.