After an introduction about the mobility of workers under the Covid crisis and its tax implications (section 1), the article begins by providing at section 2 a general overview of Art. 15 § 1 which attributes taxing power to the country where the activities are carried out as well as to the country of residence of the worker, creating a potential situation of double taxation. The article goes on at section 3 to provide an overview of the very relevant exception provided by Art. 15 § 2 which spells out the requirements under which the mobile worker is taxable only in the country of residence thereby preventing double taxation and simplifying tax compliance for the mobile worker. The article at section 4 develops a discussion of the so called ‘hiringout of labor’ which is pursued through aggressive tax structures that abuse the benefit of exclusive taxation provided by Art. 15 § 2. The paper after a digression about the wider concept of tax migration and exit taxes (section 5), concludes briefly discussing the impacts that the recent Covid crisis might have had on the system of tax treaty rules about the mobility of workers (section 6).