Poland's main private channel TVN and radio stations went off air and newspapers blacked out their front pages on Wednesday to protest against a proposed advertising tax for non-state outlets.

"This is where your favourite programme was supposed to be," read a white message on a black background on the TVN24 news channel.

In a statement to AFP, the channel, owned by the US group Discovery, said the government proposal had "the intention of restricting their pluralism and freedom of expression".

The front pages of dozens of national newspapers including the most widely read dailies Fakt and Gazeta Wyborcza had a message in white on a black background reading "Media Without Choice".

Their websites were also blacked out.

Radio stations also suspended service, with Radio Zet informing its listeners that the tax would mean "liquidation for some media businesses".

"There is no free country without independent media. There is no freedom without freedom of choice," the radio station said.

The new tax, which is expected to take effect later this year, imposes a levy on advertising revenues of television and radio broadcasters, print outlets and internet media companies.

State media are exempt from the tax.

Polish Prime Minister Mateusz Morawiecki has said the tax is part of Europe-wide efforts to tax global tech giants like Google or Facebook but many independent media outlets say they would be unfairly targeted too.

Morawiecki has said it is a "solidarity fee" that will "create better conditions for the development of free media" and help fund public healthcare and the culture sector.

But the tax comes at a time when many media companies are already hit by shrinking advertising income and a loss of revenue from other business because of the pandemic.