Calling another repository directly from a service?

I am working on a project with a service, repository pattern. AService, ARepository, BService, BRepository. Now, however, it happens that A has a relation to B. So I have to shoot another query against the B database to merge both objects later. For example: give me all objects A and their relation to object B. Can I call the BRepository directly from the AService or should I better go via the BService? Is there a rule here according to cleanCode?