Well it's a real (if secret) court, so I assume it would be what normally happens for contempt of court.
[1] https://www.eff.org/deeplinks/2013/06/government-says-secret...
More broadly though, I don't understand how you can possibly have secret courts. Justice not only must be done but must be seen to be done, otherwise its not justice.
They are about masking injustice behind the veil of "law".
Since US is a country with long tradition of rule of law. The easiest way of subverting the rule of law is by subverting the concept of a judge and of a court.
There.
I don't understand how you can have secret courts either. It's a perversion of what this country was founded upon.
Edit: Way to mind-meld on the comments, team. Holy crap.