In my opinion, this is an opportunistic money grab by the Turkish government (legitimate or not, I can't say). Turkey has historically had a serious problem collecting taxes and has been trying to clamp down recently. This is based on my own anecdotal evidence as a first-generation Turk living in the US - I wish I could provide statistics, but a quick search did not bring anything up for me.

There is a large 'informal' economy consisting of shopkeepers, street vendors and other small businesses that are not registered and avoid paying taxes completely. In the last few years, Turkey has been trying to cut down on this by requiring all businesses (including street vendors) to produce a receipt that shows they charged tax. They regularly send 'undercover' government officials to make purchases from these vendors to test if the business offers a receipt and give heavy fines if they do not.

One time, after I tried to purchase a bottle of water and declined a receipt, the shopkeeper grabbed my arm, shoved the receipt into my palm, and demanded I take it. After that, I got into a conversation with him about taxes (he said less than 10% of citizens pay, although that seems low) and, when I described the IRS and how it was a crime in the US not to pay taxes, he was shocked and wished Turkey had a similar system. He laughed out loud when I said you could go to jail for not paying taxes.