The Federal Constitutional Court in Karlsruhe was to consider if the Lisbon Treaty is unconstitutional because it takes away power from Germany's parliament, the Observer reported.
The court scheduled a two-day hearing on the matter, which analysts said was an exceptionally long time for the body and was an indication that the issue was being taken very seriously by jurists.
The Observer said the constitutional challenge was brought by Peter Gauweiler, a conservative member of the Bundestag, as well as by left-wing deputies from Die Linke political party.
Gauweiler says the Lisbon Treaty means legislation rejected by the Bundestag may still become the law of the land if the European Commission and other EU states approves it.
EU analysts said that if the challenge is upheld by the court it would be a big blow to Chancellor Angela Merkel, who strongly supports the Lisbon Treaty, and to the treaty's ratification process.
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