We study corporate income tax competition when firms operating in multiple jurisdictions can shift income using financial planning strategies. Several such strategies, particularly intra-corporate lending, appear to be actively pursued by companies to reduce subnational corporate taxes in Canada. A simple theoretical model shows how interjurisdictional tax planning can give rise to asymmetries in jurisdictions' tax policies, with one jurisdiction becoming a tax haven to attract taxable income through financial transactions, while others set higher statutory rates. Further, increased competition from tax havens may paradoxically lead to tax increases by high-tax jurisdictions. Analysis of data from administrative tax records suggests income shifting has pronounced effects on provincial tax bases in Canada. According to our preferred estimate, the elasticity of taxable income with respect to tax rates for tax shifting firms is 4.3, compared to 1.6 for other, comparable firms.