These contracts are illegal on the grounds of public policy.

Building permanent blinds is illegal on almost all public lands.

In some countries, like Turkey, prostitution is legal if done with a license from the government but illegal on the streets.

Parking is illegal on most of the community's side streets.

Those drugs are illegal on a lot of worlds.

To my mind, these deals should be illegal on their face.

"You know that chewing gum is illegal on the station."

So it's a bit of an own goal to say that images are illegal on those grounds.

I tried to help them-but that is illegal on Earth.

This was done because the wings were illegal for use on German roads.