Visitors to the Art Institute already are asked to pay $12.

But that’s voluntary.

People can pay as little as a penny and still get inside.

Now the museum is hoping to make that admission fee a mandatory thing for adults.

Spokeswoman Erin Hogan confirms the museum has presented a proposal to the Chicago Park District.

The museum would still have free days, though those would shift from all day Tuesday, to Thursday evenings.

The Park District Board is expected to vote on the proposal tomorrow afternoon.