Spain's commercial calls must use the 400 prefix from Saturday, 17 October

What changes on Saturday

From Saturday, 17 October 2026, companies that call people to sell products or services in Spain must use nine-digit numbers that begin with 400. The obligation comes from the Customer Service Act (Ley SAC), which the Ministry of Consumer Affairs promoted. Calls from 400 numbers are one-way, so recipients can take the call but cannot dial back, a rule meant to prevent fraud linked to returning calls to unknown numbers. Telecom operators will block commercial calls from numbers without the prefix, using traffic patterns such as a very high volume of calls. Companies must also keep at least two separate numbers, one for customer service and one for sales.

Who is covered and what stays exempt

The Customer Service Act applies to companies with more than 250 employees or more than 50 million in turnover, as well as to providers of essential services such as electricity, water, gas, telecoms, banking and transport. Small electricity, gas and telephone providers with national market shares below 5% are exempt. Customer service calls about ongoing contracts can be made from short numbers, the free 800 and 900 ranges or geographic numbers. The law also declares null any contract signed during unsolicited calls. Companies must renew each customer's consent every two years if they want to keep calling, and the law bans additional-rate numbers as a way to contact customers.

Practical effects for recipients

A missed call showing a 400 number cannot be returned, so recipients must decide from the number shown whether to answer. Calls to existing customers about ongoing contracts will come from geographic, 800 or 900 numbers instead. Consumers should therefore be able to identify a sales call before picking up, which is the stated aim of the change. The measure applies from the first day of the rule, with no transition period set out in the articles reviewed.

Reporting and enforcement

Consumers who receive a commercial call from a number without the prefix, such as a landline, a 900 number or a mobile, can complain to the Office for User Attention in Telecommunications (OAUT) or file a report with the Comisión Nacional de los Mercados y la Competencia (CNMC). A complaint can also be sent to the Spanish Data Protection Agency. The consumer ministry has just opened a file against a telecom company over abusive contract clauses. The consumer group OCU has warned about the limits of the new prefix.

The 400 prefix does not guarantee that calls are legal, nor does it by itself eliminate phone spam.

The OCU has asked for a public register that shows which company stands behind each 400 number, which it says would make complaints and sanctions easier.

The wider anti-spam plan

The 400 prefix is the latest step in the anti-scam plan against phone and SMS fraud launched in 2025. Minister for Digital Transformation and Public Function Óscar López announced the measure, which complements that plan. Since 15 September the CNMC has run a registry of alphanumeric aliases that companies and public bodies use to send SMS, MMS and RCS messages. Operators have blocked more than six million messages since September for using an unregistered alias or a registered alias without being its holder. The ministry says the plan has blocked more than 400 million calls and nearly 32 million fraudulent messages.