Six top executives of a media group controlled by a former ally of Prime Minister Viktor Orban have unexpectedly resigned after their boss said he was turning against the government.

Chief editors, subeditors and a deputy CEO of news channel Hir TV, Lanchid Radio and daily newspaper Magyar Nemzet said Friday that they were resigning for "reasons of conscience."

Their decision came after Lajos Simicska predicted a "total media war" against the government because planned changes to the advertisement tax could increase costs for his media group, while lowering costs for others.

The government said it was changing the tax after warnings from the European Union that it was unfair and affected competition.

Simicska, Orban's former university friend, was briefly head of the national tax authority during Orban's first term.