KHNP won the contract last summer after beating EDF in the tender, but the French giant filed an appeal with the Czech antitrust watchdog UOHS.

When the UOHS rejected the appeal last week, EDF filed a lawsuit.

The regional court in the second Czech city of Brno said it had "issued a pre-emptive ruling banning the signature" originally scheduled for Wednesday.

It added that if the deal were signed, EDF would lose a chance to compete for the contract for good even if the court ruled in its favour later on.

The tender concerns the southern Czech nuclear plant of Dukovany run by the state-run CEZ group.

The Czech Republic, an EU member of 10.9 million people, relies on nuclear power -- produced by Dukovany and the Temelin plant also in the south -- for 40 percent of its electricity consumption.

With the two new units and small modular reactors due to be built by 2050, the share of nuclear energy is expected to rise to 50 percent as the country shifts from burning fossil fuels to greener technologies.

EDF said it protested against the tender because it wanted to make sure the selection process was fair and transparent.

EDF also insists it can offer 60 percent of the value of the contract to Czech companies, while the share offered by KHNP is lower.

Czech Prime Minister Petr Fiala said after the tender that KHNP's bid was "better in all criteria assessed".

CEZ insisted on Tuesday that the tender was "fully transparent in all phases" and called on EDF to make its bid public to "rule out any doubt" that KHNP's bid was better.

The UOHS also earlier rejected an appeal by US-based Westinghouse, eliminated from the tender in January 2024 over flaws in its bid.

KHNP has offered to build the two new units for around 200 billion Czech koruna ($9 billion) each.

Prague expected to finalise the deal with KHNP by March 2025, but the EDF appeal delayed the process.

CEZ expects construction to begin in 2029 and the first new reactor launched in trial operation in 2036.

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