Holles joined Shaftesbury in opposing the 1675 Test Oath Act, which required members to swear an oath of non-resistance to the Crown. He did so on the grounds Charles had no right to require such measures, since they were 'contrary to law' and his demands for restrictions on the monarchy were resented by the court. He was dismissed from the Privy Council in 1676, after arguing Parliament could dissolve itself, rather than it being a right confined to the king, then restored during the Popish Plot in 1679, when Charles sought to reach out to his opponents.