The appeals are a potential sticking point for the Czech Republic's largest-ever energy investment as it seeks to expand nuclear energy as coal-fired power plants are de-commissioned.
The Czech government in July picked Korea Hydro & Nuclear Power (KHNP) to build two new nuclear power units, and possibly more, choosing it over France's EDF in the final tender round.
U.S. group Westinghouse also put in a bid, but was not invited into the final phase of the process.
A spokesperson for Czech anti-monopoly office UOHS said it would study the appeals.
"EDF seeks to ensure that the tender process adheres to the principles of fair trade and transparency," the French company said in a statement, adding that its offer remained valid.
Westinghouse said it had appealed on the grounds that KHNP did not have a licensing agreement to export its reactors, which are based on Westinghouse technology.
That has been the subject of ongoing international arbitration, and Westinghouse said a decision from that process was not expected before the second half of 2025.
KHNP said in a statement it "will respond sufficiently to the dispute with Westinghouse to avoid negative impacts on the Czech nuclear project".
The Czech Republic has sought to finalise contract details with KHNP by the first quarter of next year.
CEZ (CEZP.PR), opens new tab, the 70%-state-owned Czech energy company running the tender, said it had also received objections from bidders and was ready to provide answers to UOHS, although it believed it was not possible to challenge the tender on competition grounds due to a national security exception.
UOHS said it would examine whether the appeals were admissible.
Governments have long sought to build up the Czech nuclear power fleet to replace both coal and ageing current plants. A previous tender was abandoned in 2014.
The price for one new 1,000-megawatt KHNP-supplied unit when building two at the same site was estimated at 200 billion crowns ($8.9 billion) at current prices, the government said last month.
CEZ aims to start construction of the first of two new units at its Dukovany nuclear power plant later this decade, with expected completion in 2036. Two more units at its Temelin plant could possibly be added later.
