A Minneapolis police officer who worked off-duty security at a Cub Foods store is under investigation and a group of store employees were fired after they were caught misusing a store rewards card to get discounts on gas, the store and police said Thursday.

The employees, who all worked at the W. Broadway Cub Foods store, allegedly used other customers’ purchases to ring up credit with the My Cub Rewards Card program for gas discounts at Holiday Station stores, a Cub spokesman said.

Customers typically earn gasoline discounts of five cents per gallon for every $50 spent at Cub Foods, with a maximum discount of $1.50 per gallon.

The fired employees targeted customers who did not use a Rewards card, swiping their own cards to get credit for the sale.

It’s unclear what role the police officer played; officer William Gregory, who worked at the W. Broadway Cub Foods in north Minneapolis, is the subject of an internal affairs investigation, according to a spokesman for the Minneapolis Police Department, who declined to explain further.

The employees were fired this month, said Cub Foods spokesman Luke Friedrich. He did not specify how many employees were let go.