Prime Minister Recep Tayyip Erdogan says the reforms, overhauling the judiciary and making the army answerable to civilian courts, are designed to help meet requirements for Turkey to join the European Union.

Secularist critics see the reform package as an attempt by Erdogan's AK Party to seize control of all levers of the state and undermine Turkey's secular principles.

The Constitutional Court has struck down several key AK Party reforms in the past, prompting concerns about political stability. Investors are following developments, although on Friday assets firmed, boosted by positive sentiment in global markets.

Erdogan, who faces an election set for 2011, has said he will not call a snap poll in the event the court annuls the referendum, but analysts have said such a ruling could paralyze decision-making and galvanize the opposition.

Prospects for AK Party winning a third term in office are unclear, but markets would certainly be wary of any return to the fragmented, warring coalitions of the 1990s. Last weekend, the opposition Republican People's Party (CHP) formally jettisoned its hard-line leader Deniz Baykal, rejected by voters in 2002 and 2007 polls, and elected former civil servant Kemal Kilicdaroglu in his place.

Critics suspect the AK, or Justice and Development Party, of aiming to place its own supporters within the senior judiciary.