WARSAW, Oct 18 (Reuters) - Poland is a loyal member of the European Union but opposes excessive centralisation of power, Prime Minister Mateusz Morawiecki said on Monday in a letter to other European leaders amid a deepening row over the rule of law. Brussels has long said reforms introduced by Poland"s right-wing government undermine judicial independence, but their row escalated this month when the Polish Constitutional Tribunal challenged a key tenet of EU integration by ruling that parts of the European treaties were incompatible with the constitution. This fuelled talk of a potential "Polexit", but Morawiecki says his government has no intention of following Britain"s example and taking Poland out of the EU. "I would like to reassure you that Poland remains a loyal member of the European Union," he wrote in the letter, which was published on a government website on Monday. However, Morawiecki warned against of a "dangerous phenomenon that threatens the future of our Union". "I mean the gradual transformation of the Union into an entity that would cease to be an alliance of free, equal and sovereign states - and become one, centrally managed organism, governed by institutions deprived of democratic control." In a move sure to further raise tensions, Polish Justice Minister Zbigniew Ziobro urged his government on Monday to take legal action against Germany over what he said was a politicised system of choosing judges in the bloc"s largest nation. EQUALITY Ziobro, architect of Poland"s judicial overhaul and leader of an arch-conservative junior partner in Morawiecki"s government, has often complained of what he sees as the EU"s unequal treatment of Poland. "Since the EU is based on the equality of all states and citizens, it is necessary to check the situation in Germany, where the selection of judges to the counterpart of the Supreme Court is entirely political," Ziobro told a news conference. Ziobro said that while top court judges in Germany are selected by politicians, in Poland judges themselves are more responsible for the selection process. However, critics say that the body that appoints judges in Poland has come under political influence. The German government"s press office and a Polish government spokesman did not immediately reply to requests for comment. Laurent Pech, professor of European law at Middlesex University, London, said references to the situation in Germany were "irrelevant". "The references to the situation in Germany or elsewhere should be seen for what they are: to distract Polish citizens from the repeated violations of the Polish Constitution in order to create a de facto autocratic one-party system where judges and prosecutors can be punished at will." Poland"s government says its judicial reforms are necessary to remove the vestiges of communist rule in the country.