Which of the following actions is prohibited in a lawyer's litigation conduct?

The action of submitting motions that prolong proceedings unnecessarily is prohibited as it goes against the ethical obligations of a lawyer to promote fair and efficient litigation. Lawyers have a duty to the court and their clients to ensure that legal proceedings are handled in a timely manner. Engaging in practices that deliberately extend litigation without just cause can waste valuable court resources, increase litigation costs for clients, and impede the administration of justice.

In contrast, engaging in good faith arguments for law change is permissible as it reflects a lawyer's duty to advocate on behalf of their clients and contribute to the development of the law. Scheduling court appearances, while it can be excessive if unwarranted, is not inherently prohibited if there is a legitimate reason for each appearance. Direct negotiations with opposing parties, as long as notification is given to other counsel, are also pertinent to effective practice and are not inherently unethical. Therefore, the act of unnecessarily prolonging proceedings through motions is the clearest violation of ethical duties in this context.