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This paper aims to demonstrate empirically the existence of strategic tax interactions between the decisions of local authorities in the Nord-Pas de Calais region. Our approach consists in calculating the gradient of the best-response function linking the rate of local business tax in one commune with the different rates in rival authorities by means of a spatial autoregression model. We show that in some cases the hypothesis of tax interactions is confirmed; local authorities do not set their local business tax rate freely but are influenced by the choices of neighbouring communes, especially in urban areas of employment.