The only way this would be acceptable is that they would give a credit for the $1.50 when you redeem the punch card. I would have said, "No, thanks."
We have a grocery store that started a "bonus" for customers. They give points for a discount on gas, but it has strings attached. One is that only 2 gas stations honor them and they are not convenient. Another is that they expire at the end of each month. Too much confusion and trouble for an old lady like me to mess with.