Prague  - The Czech Republic's Constitutional Court on Tuesday opened a hearing on a challenge to the European Union's reform Lisbon Treaty in a case widely expected to clear the way for the EU's grand reform aimed at boosting its global clout.

Czech President Vaclav Klaus, a treaty opponent whose signature is the last one needed before the pact becomes valid, is not allowed to ratify it before the court rules in the case.

It remains unclear whether the court will issue a verdict on the same day or adjourn the proceedings. Czech Prime Minister Jan Fischer has said that he does not expect the court to rule Tuesday given procedural steps that lie ahead.

The challenge to the treaty was lodged by 17 Czech senators, Klaus followers and Lisbon critics, who view the pact as a threat to national sovereignty and a tool that would turn the 27-member bloc into a superstate.

The accord's supporters, however, see the new rules as a key to improving the bloc's global standing by streamlining its decision-making.

The pact introduces an elected EU president and a de-facto foreign minister. It strips member countries of veto rights in most fields.

The top Czech court, based in Brno, the Czech Republic's second-largest city, is reviewing the Lisbon Treaty for the second time. Its 15 judges ruled in November 2008 that several sections of the pact were "not at odds" with the Czech constitution.

However, the latest case poses only one hurdle to the accord's entering into force.

In a separate last-minute obstacle, Klaus has demanded that the Czech Republic receive an exemption from the EU's Charter of Fundamental Rights, a part of the treaty that he views as a threat to Czech citizens' property rights.

He has claimed that the rights charter would enable ethnic Germans expelled from former Czechoslovakia after World War II to sue for their confiscated property in European courts.

EU leaders are set to deal with the Klaus opt-out at their quarterly summit in Brussels on Thursday and Friday. (dpa)