This study investigates how strategic tax transfer pricing of a multinational company (MNC) and two tax authorities in different countries affects production and tax avoidance decisions at the firm level and tax revenues at the country level. We employ a game-theoretical model to analyze the costs and benefits of two tax transfer pricing regimes (consistency vs. inconsistency) under asymmetric information. Though tax transfer pricing harmonization is considered a promising instrument to fight undesired tax avoidance, the implications are largely unclear. We find tax avoidance in equilibrium in both countries under inconsistency. Surprisingly, we identify conditions under which low-tax countries benefit from consistency while high-tax countries benefit from inconsistency. This explains how the strategic interaction of taxpayer and tax authorities under firm-level heterogeneity challenges the implementation of consistent regimes. Understanding the implications of (in)consistent transfer pricing rules is crucial when reforming transfer pricing regulations to fight tax avoidance and double taxation.