Ahh, the weekend. The perfect time to knock a few items off the old to-do list: run to the grocery store, make a trip to the hardware store, buy a new car.

Not so fast. Not on Sunday!

Since the 1980s, it’s been illegal for car dealerships to operate on Sundays in Illinois.

Why?

Well, some owners and employees wanted to shut down to spend time with their families or for religious reasons, but — and pay attention, this is the key — they didn’t want their competitors to be open and have the chance to steal business.

The first attempts to close down dealerships on Sundays date back to the ‘50s and ‘60s, but those laws never made it off the lot; they were vetoed or struck down in the courts.

But since 1984, Illinois car dealers must close their doors on Sundays.

Illinois isn’t alone. A dozen other states don’t allow Sunday car sales either. It’s a vestige of so-called “blue laws” barring certain activities on the basis of religion — like say, buying a sports car on the sabbath.

The religious angle is one reason Illinois’ ban has been challenged multiple times. One alternate proposal still restricted car sales to six days a week but allowed dealerships to pick which day they take off, since, for example, Jews and Muslims don’t observe a day of rest and prayer on Sundays.

Some pro-business groups argue the law restricts free commerce.

But so far, Illinois has kept the Sunday car sale ban on the books and would-be test drives off the roads.

So if you’re looking for a hot deal on a new set of wheels, you’ll have to look on another day.