What's a polite term for a cartel?

The legal profession is a guild in the sense of a trade association where all the members have the same interests and that call for levels of knowledge for admission (law school, bar exam). Anyway, they are a cartel. A cartel is an economics term but also used by Jacques Lacan to describe a closed group of individuals working together on a psychoanalytical issue. That said, it has broader usage. There is a very interesting discussion on the broader meaning of cartel as also applying to lawyers.

There is a book called Overcoming Law that is all about this.

The law is not a cartel, it's a regulated profession. That's not an official term, but lawyers, like architects, like doctors, are individuals who are supervised by regulatory authorities (in the case of lawyers, usually a bar association) that can set requirements for entrance into the profession, Continuing Legal Education, and apply discipline, including suspending or rescinding a lawyer's license to practice law. Lawyers are not a unified group and they're not all private lawyers with businesses like law firms. They are not able to band together and fix prices, as do cartels, which are often illegal. Public defenders, for example, work for the government, as do prosecutors. They are civil servants.

A cartel by contrast, means:

1: a written agreement between belligerent nations

2: a combination of independent commercial or industrial enterprises designed to limit competition or fix prices

3: a combination of political groups for common action

Merriam Webster