RTL Germany, ProSiebenSat.1 Media and United Internet will work with WEB.DE and GMX. Zalando to develop an online registration and log in service in line with EU data protection law, they said in a statement.
The alliance will allow the group's current 45 million users to log into partner websites securely, with transparency over how their data is used, it said.
An open standard will allow users to access all the initiative’s online services using the same log-in data instead of having to repeatedly log in using different data each time.
A privacy centre will allow users to manage their profile data, change their password and issue or revoke consent.
User data is shared between account providers and services only after the user has given consent. Repeated manual data entries and different passwords will no be longer needed, reducing the risk of forgetting log-in data.
Other partner companies are welcome to join, the organisations said, and any online service can use the open single sign-on service. Data will be stored by the account provider in the EU and regular auditing will take place, the group said.
Thomas Ebeling, chief executive of ProSiebenSat.1 Media SE, said: "The initiative has been deliberately designed as an open standard. Other companies are more than welcome to join us."