Actually, it's walking on thin ice. The right to assemble is guaranteed in the first amendment, and implicit in that is the right to travel. It can be argued, quite rationally, that travel by plane is part of that. I want to travel to Hawaii? Sure, you could take a boat and spend a week round trip in transit, but that's quite a penalty.
And what stops a nefarious government from starting a "no public transit" list? And if they revoke your drivers license? Where do we draw the line? What if we're in a not-too-distant future where private ownership of cars is a thing of the past and you can be denied any travel that you can't walk to?