from selling gas for less than what they paid the wholesaler for the gas. So until a gas station gets a delivery of gas for a cheaper price, they can't lower their prices. And if they hedged against rising prices by contracting to buy gas in the future at a certain price, they are stuck selling at that price until their contract has expired and they buy gas at the new lower price.
This law is why gas prices change much more slowly in Utah than in most states. IMHO, this is a law that should be repealed.