Cash payments of more than 2,500 Euro illegal
The law is already older, but is not yet known to many foreigners in Spain: All cash payments in payment transactions with companies are limited to an amount of 2,500 Euro. Amounts of more than 2,500 Euro must be paid in the form of checks or transfers. Denominations are also forbidden.
One exception to this rule exists for persons who have their main tax domicile outside of Spain (non-residents). They may still pay amounts of up to 15,000 Euro in cash. The Spanish Government had already enacted the law in 2012 to combat the informal economy.