http://revach.net/article.php?id=1564

Section: Halacha   Category: Tshuvos
Rav Shlomo Zalman Auerbach: How To Deal With A Crooked Grocery Store
Clearly, if you see someone stealing you must report them to the police.  What happens if you see that the local grocery charges more than the legal price for staple food items that are under price control by the government?  (See Choshen Mishpat 231:20-21) May you report this to the proper authorities?  Is this considered the same as stealing that it allows such drastic measures?

Rav Shlomo Zalman answered that although reporting may be scary and unpleasant nevertheless this is a breach of the market pricing (Mafkia She'arim) and reporting is in order. (Aleihu Lo Yibol CM 15)

Disclaimer: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.