Differences between prices of goods indicated on a shop shelf label and prices actually paid by a client at a cashier’s desk was considered an unfair market practice.
https://decyzje.uokik.gov.pl/bp/dec_prez.nsf/43104c28a7a1be23c1257eac006d8dd4/c3c9bf6b79d1dc2ac12585ce0038fe73/$FILE/DECYZJA_NR_RBG_-_6_2020%20(1)%20(002).pdf