  The perovskite oxynitride LaTiO\textsubscript{2}N is a promising material for
photocatalytic water splitting under visible light. One of the obstacles
towards higher efficiencies of this and similar materials stems from
charge-carrier recombination, which could be suppressed by the built-in
electric field in polar materials. In this study, we investigate the
spontaneous polarization in epitaxially strained LaTiO\textsubscript{2}N thin
films via density functional theory calculations. The effect of epitaxial
strain on the anion order, resulting out-of-plane polarization, energy barriers
for polarization reversal and the corresponding coercive fields are studied. We
find that for compressive strains larger than 4\% the thermodynamically stable
anion order is polar along the out-of-plane direction and has a coercive field
comparable to other switchable ferroelectrics. Our results show that strained
LaTiO\textsubscript{2}N could indeed suppress carrier recombination and lead to
enhanced photocatalytic activities.

Materials Science