Hungary's parliament on Tuesday approved legal amendments restricting access to public information about the state-owned postal services, and businesses and foundations established by the National Bank of Hungary.

The proposals were endorsed by lawmakers from Prime Minister Viktor Orban's Fidesz party despite warnings from critics, including the country's freedom of information watchdog, that some of the changes could be unconstitutional.

The post office, for example, will no longer be required to divulge public data if it or its enterprises were to suffer "disproportionate damages" should the information provide an advantage to competitors.

The central bank, meanwhile, will be able to reject public information requests about its foundations — set up at a cost of around 250 billion forints ($875 million) — and business units. In recent years, the bank has greatly increased its real estate holdings and also has been criticized for its abundant spending on artworks.

Critics say the changes greatly limit the transparency of state institutions, further weakening the system of democratic checks and balances.

Attila Peterfalvi, head of the National Authority for Data Protection and Freedom of Information, said in a letter to parliament's legislative commission that the restrictions on central bank information were too broad and needed to be defined more precisely. He also rejected the widely-derided attempt by Fidesz to justify the restraints by claiming that public funds given by the central bank to its foundations "lose their public nature."

Peterfalvi also said that provisions making the new rules apply to information requests already approved or being considered by the courts amounted to "legislative backdating," which could interfere with judicial independence.

Investigative journalists said the new rules would have a "very negative" effect on their work.

"In recent years, it was clear that information about most suspected corruption cases could only be obtained with public information requests," said Tamas Bodoky, chief editor of the atlatszo.hu news website. "This is what they want to eliminate with these laws."

Tuesday's amendments also more than doubled the salary of central bank chief Gyorgy Matolcsy to 5 million forints a month ($17,500), with other top bank officials receiving proportional raises.