I ain't no lawyer, but I presume this is a case involving contract law, not civil rights. I can't recall ever in my life hearing any lefty say that a company or entity can't sue in court to enforce a contracts, or on the basis of contractual law.
As far as I know contract law has been standard practice in the United States for over 200 years.
Is contract law on the same level as freedom of speech or freedom of religion? Just trying to clarify. Was that your point?
No, it's civil rights. You could make the argument that civil rights are not primary because Congress overstepped its legitimate powers in passing a bill of attainder. But the bill of attainder clause is, obviously, there to protect rights to due process.