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