The molecular structure of the title compound, NH₄⁺·C₇H₇O₄S^-, is featureless [the methoxy C atom deviating 0.173 (6) Å from the phenyl mean plane] with interatomic distances and angles in the expected ranges. The main feature of interest is the packing mode. Hydrophilic (SO₃ and NH₄) and hydrophobic (PhOCH₃) parts in the structure segregate, the former interacting through a dense hydrogen-bonding scheme, leading to a well connected two-dimensional structure parallel to (100) and the latter hydrophobic groups acting as spacers for an interplanar separation of c/2 = 10.205 (2) Å. In spite of being aligned along [110], the benzene rings stack in a far from parallel fashion [viz. consecutive ring centers determine a broken line with a 164.72 (12)° zigzag angle], thus preventing any possible π–π interaction.