Judging or ruling according to other than what Allaah has revealed is contrary to faith and Tawheed, which are Allaah’s rights.
“Have you seen those (hypocrites) who claim that they believe in that which has been sent down to you, and that which was sent down before you, and they wish to go for judgement (in their disputes) to the Taaghoot (false judges, etc.) while they have been ordered to reject them. But Shaytaan wishes to lead them astray. And when it is said to them: ‘Come to what Allaah has sent down and to the Messenger,’ see they hypocrites turn away from you (Muhammad) with aversion.” [al-Nisaa’ 4:60-61]