Berlin - Germany's Federal Constitutional Court began deliberating Tuesday on the legality of planned reforms to the European Union contained in the controversial Lisbon Treaty.

Critics of the treaty - which has already been rejected once by voters in Ireland - argue that it transfers too many responsibilities to the EU, thus reducing Germany's sovereignty.

The petitioners include Peter Gauweiler, a maverick federal deputy in Bavaria's Christian Social Union (CSU), and former EU parliamentarian Franz Ludwig Graf von Stauffenberg, also of the CSU.

The federal government, defending the treaty, is being represented at the Karlsruhe-based court by Interior Minister Wolfgang Schaeuble and Foreign Minister Frank-Walter Steinmeier. The hearing is expected to last two days.

The document was approved last year by both chambers of the German parliament, but still needs a signature from German President Horst Koehler to complete its ratification.

If the constitutional court rules against the treaty, due to be implemented in 2010, this would prevent its ratification in Germany and would likely sound a death knell for the future of the reform processes contained within it.

The treaty has been imperilled since it was rejected by Irish voters in a referendum, the only one of EU's 27 states to put the plans to a public vote. Ireland is expected to vote again on the issue later this year.

The Lisbon Treaty replaced the earlier proposed EU constitution, which was rejected by French and Dutch voters in referendums in
2005.

The treaty would, among other reforms, create a post of president of the European Union, and a permanent high representative for foreign affairs, and bring in more qualified majority voting.

Koehler's functions are mainly ceremonial, but he has sometimes used his limited powers to block government legislation. (dpa)