ANKARA (Reuters) - Thousands of anti-government protesters marched in Turkeys capital on Sunday, calling on Prime Minister Tayyip Erdogan to resign for what they say are violations of the countrys secular principles. About 20,000 people waving red-and-white Turkish flags and carrying banners reading Secular Turkey will stay secular walked from the central square of Tandogan to the mausoleum of Mustafa Kemal Ataturk, founder of the modern Turkish Republic. Demonstrators also protested the governments handling of the economy as unemployment reaches a record high amid the global economic downturn. Some denounced the so-called Ergenekon probe into a suspected nationalist group accused of conspiring to topple Erdogans government. Erdogans opponents have said he wants to make Turkey more overtly Islamic through incremental steps, like failed attempts to end a ban on the Islamic-style headscarf at universities. The ruling AK Party narrowly escaped a ban last year on charges it was undermining Turkeys secular constitution. Erdogan has pledged to amend the constitution to reform the judiciary and make it more difficult to close a political party on ideological grounds. Critics of the governments proposed changes say they would threaten the nations founding principle of secularism. Turkeys population of 71 million people is 99 per cent Muslim, but the state strictly controls religion. May the hand that touches the judiciary break, some banners said at the Sunday march. The European Union has said Turkey must reform its national charter to guarantee human rights like freedom of religion and expression if it is to make progress in its membership bid. The Ankara march was organised by the secularist Ataturk Thought Association, which has been implicated in the Ergenekon investigation. The indictment in the Ergenekon case says a series of protests organised by the association in 2007 were part of an illegal attempt to topple the government. Millions of people staged rallies in 2007 to protest the governments choice of Abdullah Gul as President. Erdogan then called early elections after the secularist military also expressed reservations about Guls candidacy. The AK Party went on to win the July 2007 election by the biggest margin in four decades, and the new parliament elected Gul president the following month.