Czech senators opposed to the EU's Lisbon Treaty have filed a new complaint against it with the country's constitutional court.
The complaint could create a new delay to treaty ratification, even if Irish voters back the treaty in a referendum on Friday.
Czech President Vaclav Klaus, a Eurosceptic, says he will not sign the treaty until the court decides.
The treaty cannot take effect unless all 27 EU member states back it.
The Czech court has rejected previous complaints about the treaty, which is aimed at streamlining EU institutions to improve decision-making in the enlarged bloc.
