Where did you get that info? Not that I am disputing it, just interested in researching those things.
Here you are, in Polish only unfortunately - wp.pl/?s=finanse.wp.pl%2Fsgwpsgfirst-6322120390408321a
The Sunday ban really screwed up small shops, because the large chains introduced good promotions on Fridays/Saturdays only, so people are now staying at home on Sunday and not using any shops.