Optimal Tax Administration Responses to Fake Mobility and Underreporting

In a two-country model, the citizens of a ‘big home country’ can either fictitiously move residence to a ‘small foreign country’ where residence-based taxes are lower (external tax avoidance), or under-report the tax base at home (internal tax avoidance). Tax setting is the result of Cournot-Nash competition between revenue maximizing governments, with the home government also setting two types of administration policies, one for each form of tax avoidance. We show that although it is optimal to employ both types of administration policies, which in themselves are both effective at tackling the targeted form of tax avoidance, the optimum is characterized by a tradeoff in terms of policy outcomes: either internal avoidance increases and external avoidance decreases, or the opposite, depending on the characteristics of the fiscal environment.