Article 49(1) EC precludes a national provision of tax law such as the one in the present case, according to which non-resident financial institutions are subject to tax on interest arising within the territory and, unlike resident financial institutions, have no possibility of deducting operating costs directly linked to carrying on the financial activity. The costs which have a direct link to carrying on an activity include a share of the taxpayer's overheads, to the extent that those costs are necessary for carrying out the taxed activity. The costs are to be taken into account in the amount of the costs actually incurred.