Because of a complain letter?

Malaysia Today

What happened was that the Chief Justice had a home next door to the Agong’s and His Majesty’s house was under renovation. The Chief Justice was displeased with the noise and pollution and he wrote a letter to the Agong with copies to all the Rulers complaining about the matter. The Agong was upset with this insolence on the part of the Chief Justice. Writing a complaint letter is one thing and could be forgiven since this was a genuine grievance -- though an audience would have been the correct protocol instead of a complaint letter -- but to copy the letter to all the Rulers smacks of pressure.

The Agong was outraged and demanded that Mahathir sack the Chief Justice for this insolence that tantamount to misconduct. Mahathir, however, replied that he does not have the authority to sack the Chief Justice and that this can only be done through a Tribunal. The Agong then commanded (titah) that a Tribunal be set up, which was to report direct to His Majesty. The Tribunal found the Chief Justice guilty of misconduct and sent its recommendation to the Agong, who then removed the Chief Justice.