The cinemas will show only soft or hard core porn films throughout the day Thursday, said Elka Drambozova, chief accountant of Sofia Film, which runs the capital's 10 main cinemas.
"So far we have been relieved from tax. Now we will have to raise prices," Drambozova said by telephone.
The cinemas do not normally show many erotic films, which unlike ordinary films are subject to a 22 percent turnover tax.
But Sofia Film says the new flat rate 18 percent VAT, due to be introduced from April 1 and levied on all films, could drive more expensive family entertainment from the screens.
Thursday's protest will coincide with the end of a four-day strike against the new tax by major newspapers.
The newspapers have already stopped reporting on parliament and the government to press their demands to be relieved from VAT, which they say will strangle the media. From Monday to Friday they will not publish at all, they say.
Finance Minister Stoyan Alexandrov has brushed off the threats, saying the tax, which is a condition for future funding from the International Monetary Fund, is essential for the budget.
Last week he said Bulgarians would be relieved to have a break from the newspapers, prompting calls for his resignation from editors on Friday.
Alexandrov has accused the papers of misleading politicians and the public by exaggerating the impact of the new tax, part of Bulgaria's moves towards a market economy.
The tax has raised fears of hyperinflation among ordinary Bulgarians, scared by signs which have already appeared in shops warning of price increases.
Finance ministry officials, who say the new taxing system should not affect at least half the goods, have warned shop owners that they will be fined if they impose unjustified price increases.
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