In place of their usual shows, the outlets ran written or spoken slogans like "This used to be your favourite programme" and "Media without choice".

Critics say Poland is following the example of central European ally Hungary in trying to increase government control over the media, an issue that came into sharp focus in December when state-controlled oil refiner PKN Orlen said it was buying German-owned newspaper publisher Polska Press.

The self-imposed 24-hour silence came a day after many publishing groups addressed an open letter to authorities to object to the planned tax, which the government says will help raise funds for healthcare and culture, both hit hard by the coronavirus pandemic.

The letter said the tax would mean "weakening, and even eliminating some media in Poland" and deepening inequalities between private outlets and public ones, which the signatories said were heavily supported by the government.

"Many publications are balancing on the edge of profitability. This additional tax could take away all of the remaining profits," Marek Frackowiak, the head of the Association of Press Publishers, told Reuters.

In particular, outlets pointed to the economic hit private media had already taken during the coronavirus pandemic.

According to the Association of Local Newspapers in Poland, the local press saw an approximate drop of 30% to 50% in advertising revenue and a 30% drop in sales since the pandemic began last year. Larger press publications also complained of a significant drop in advertising and sales revenue.

Bartosz Weglarczyk, editor-in-chief of web portal Onet, told Reuters the outlet's parent company Ringier Axel Springer could be paying 10-20 million zlotys ($2.7-5.4 million) extra a year due to the new tax, according to its calculations.

"It means media will remain on a leash and those who jump or pull too much won't get money from the government, for example, and will have to shut up shop," Bartosz Wielinski, the deputy editor-in-chief of Polish daily Gazeta Wyborcza, which took part in the campaign, told Reuters.

TV broadcasters Polsat and TVN, radio station Radio Zet and web portal Interia were also among outlets that halted coverage on Wednesday.

GOVERNMENT RESPONSE

In stark contrast to the slogans of these private outlets, public broadcaster TVP Info - which did not go off-air - ran news tickers including "Media companies don't want to share their multi-million profits with Poles" and "Media firms are treating Poland like a colony."

The government has long argued that foreign media groups have too much power in the Polish media landscape, distorting public debate.

It says the tax will benefit the whole population, and that other European countries have similar levies.

Government spokesman Piotr Muller told TVP Info that the tax could amount to anywhere between 2% and 15% of advertising income, depending on the size of the company.

(Reporting by Joanna Plucinska, Pawel Florkiewicz, Kacper Pempel and Alan Charlish: Editing by Nick Macfie, Pravin Char and Philippa Fletcher)

By Joanna Plucinska and Kacper Pempel