The court made the statement as part of a ruling in favour of the union of airport employees, which filed a suit to stop the privatisation, saying workers had not been properly consulted about the sale.
The government plans to appeal the decision, while the airport management said it would start consultations with the unions.
The highest non-binding offer received for the government's 75 pct minus one share in the airport operator was 1.5 bln eur, Finance Minister Janos Veres told a news conference last week.
The five bidders are BAA, the operator of London's Heathrow, along with Copenhagen Airports, a consortium of Germany's Deutsche Bank and Frankfurt airport operator Fraport, German construction firm Hochtief and Australia's Macquarie Airports.
The deadline to submit binding offers is November 2. The privatisation agency has said it wants to complete the sale before the end of the year.
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