Constitutional Court of Croatia

The Constitutional Court of the Republic of Croatia is an institution that acts as the interpreter and guardian of the Croatian Constitution and which monitors the conformity of laws with the Constitution as well as protection of human rights and freedoms of citizens that are guaranteed by the Constitution. It is considered to be de facto the highest judicial authority because it can overturn Supreme Court decisions on the basis of constitutional breaches. It is not considered as being part of the judicial branch of government, but rather a court sui generis, and it is therefore often colloquially referred to as a "fourth branch of government", alongside the traditional model of tripartite separation of powers into the executive, legislative and judicial branches.

Source: Wikipedia