From Saturday, 17 October 2026, all commercial telephone calls in Spain must begin with the 400 prefix . The aim is to clearly identify unwanted advertising calls and better protect consumers. The requirement is based on the Ley de Servicios de Atención a la Clientela and is being implemented by the Ministerio para la Transformación Digital y de la Función Pública .
The rules require companies to use only nine-digit numbers beginning with 400 for outbound advertising. This clearly distinguishes advertising calls from customer service numbers and other services. The Secretaría de Estado de Telecomunicaciones e Infraestructuras Digitales has allocated the corresponding number range and set technical requirements for its activation. Network operators are expected to block calls or flag them as non-compliant if they do not meet the labelling requirement.
The ministry points to a sharp rise in complaints about telephone marketing and programmes against telephone and SMS fraud that have been running since 2025. Official statements indicate that extensive filtering measures are already in place. The authorities have also announced inspections and penalties if companies or providers circumvent the new rules. According to La Moncloa, the allocation and monitoring of the new number blocks will be coordinated with the Comisión Nacional de los Mercados y la Competencia .
Minister Óscar López says the requirement gives customers a simple basis for deciding: if a landline number begins with 400, the call is commercial. This makes it easier to manage availability, for example through custom block lists or network options covering the entire number range. For businesses, the change means that contact centres and dialling software must be adapted to the new numbering in good time.
Consumer advocates welcome the improved visibility but point out its limitations. Labelling alone will not automatically reduce the number of unwanted calls. There are concerns about possible workarounds using caller ID spoofing, which can only be curbed through consistent network filtering. The government counters that the combination of clear numbering, network obligations and penalties will improve effectiveness.
The measure comes into force on 17 October 2026. It is intended to increase transparency in telephone marketing without obstructing legitimate customer contact. Legal details can be found in the resolution of the Secretaría de Estado de Telecomunicaciones e Infraestructuras Digitales and in related ministry statements.
Editor: Daniel Mayer (Article created with AI assistance).