In principle: yes. That is, as long as the agreement is not in violation of other rules/laws. Considering the role a service has in society and its market posi

In principle: yes. That is, as long as the agreement is not in violation of other rules/laws. Considering the role a service has in society and its market position, such a rule could e.g. violate anti trust law. But that's a different matter, and up to a court to decide.