The European Union warned Hungary on Friday that it faced possible sanctions over controversial constitutional changes which appear incompatible with EU legislation and the rule of law.
In a letter to Hungarian Prime Minister Viktor Orban, European Commission head Jose Manuel Barroso said an initial legal review had raised "serious concerns" over the changes, which among other things limit the powers of the key Constitutional Court and reinstate measures its judges had ruled void.
When the review is completed, "the Commission will have to take the necessary steps in order to start infringement procedures where relevant," a statement said, citing Barroso's letter.
"I strongly appeal to you and to your government to address these concerns and to tackle them in a determined and unambiguous way," he said.
"This is without doubts in the best interest of Hungary and of the EU as a whole," he added.
In a written reply late Friday, Orban said he had put legislation in motion to address Barroso's concerns.
"I reiterate the commitment of the Hungarian government and the Hungarian parliament to European norms and values and to ensure the full cooperation of my government in addressing the concerns you raised," Orban wrote.
The letters are the latest in a long series of exchanges between Brussels and Orban since he came to power in 2010 over media freedom, the Constitutional Court and control of the central bank.
Orban's Fidesz party enjoys a two-thirds parliamentary majority and the prime minister has insisted there is no ground for concern.
Last month, after parliament approved the fourth set of changes, Orban said the "Constitutional Court will continue to be the guardian of the constitution... If the European institutions see something they don't like or is against regulations, then let's discuss it."