Switzerland is unique among modern sovereign states in that the authority to levy these taxes is limited in duration and extent. The Constitution imposes an upper limit on the federal tax rates and causes the federal authority to levy taxes to expire in 2020. A renewal of that authority requires a constitutional amendment, which must be approved in a popular referendum by both a majority of the popular vote and the cantons.
If that renewal is not approved at the polls (as it has been six times since 1958), the Confederation itself will conceivably dissolve for lack of funds. All attempts to remove this limitation by amending the constitution to provide for a permanent federal authority to levy taxes have been rejected in Parliament or – no less than five times – by popular vote, most recently in 1991.
The federal constitution imposes certain limits on taxation at the federal cantonal and municipal levels. To begin with, it provides that no tax may be levied except where provided for by federal, cantonal or municipal statute. Because statutes can at all levels be made subject to a popular referendum, Swiss tax rates are in practice set directly by the voters through instruments of direct democracy.
The constitution mandates that taxation must be general and equal in nature, and it must be proportionate to one's ability to pay. The Federal Supreme Court has interpreted this as prohibiting a regressive tax, although flat rate taxes (as instituted in several cantons) are held to be constitutional by tax law scholars. Moreover, double taxation by several cantons is constitutionally prohibited, as is a confiscatory rate of taxation.