A sovereign state can enact anti-monopoly legislation, price ceilings, taxes, tax breaks, special ecoomic zones and other mechanisms as needed, free market or not.
Except Poland can't, because she signed up to the European Union which contains a lot of law designed to prevent distorting the free market. In this case, everything has to be in accordance with European law, which is why Hungary backed off on the supermarket tax.
That's precisely the guy who is going to get screwed by PISed-up economics.
Indeed. Let's not forget that the "small Polish business owner" will have no scruples about increasing their prices by the amount of the large supermarket tax and then blaming the government, even though they'll actually pay far less tax.