Not giving prior consent to belong to one of them can be a violation.
This is supported by a resolution of the Spanish Agency for Data Protection (SADP) that determines that the City Council of ....., incurred a serious offense by including a neighbor in a large group of WhatsApp without their prior authorization.
SADP said that personal information about residents of the municipality was disclosed, since their mobile phone numbers were visible to all other members.
This infraction can lead to fines ranging between 40,001 and 300,000 euros. Therefore, to avoid such situations, it is always advisable to keep in mind that you must have the express consent of any person, although there are exceptions. For example, if the group is family or friends, it is outside this regulation. For this, the SADP itself specifies that the limit is in the 20 participants.