Yes, professionals are allowed to consult with each other about their cases as long as they protect the identities of their clients meaning they don't name names and don't share any other easily identifiable information.

The cases in which such consultations might be unethical is when, f.i., one therapist is working with a couple and the other one is working with one of the partners. In those kinds of cases, they have to obtain their clients' permission to talk to each other because they both know the people they are discussing and so sharing information about them may affect both couple's and individual counseling, therefore, clients have to be informed about it. They shouldn't discuss them secretly behind their backs.

It may also be allowed for professionals to share information about a particular client if they work for the same agency and the client is receiving services at that agency. But that would also fall under category of professional consultations.