Any advice on a writer's contract payment problem?

This relates to a current television show, not in its first season, credited to a founding script writer. The named writer subcontracted for one ghostwritten episode and insisted on a NDA for the additional writer's involvement. It's now more than a year since the episode went to air and the employing writer doesn't seem to want to pay anything. Pursuing this formally would break the NDA and invalidate the contract, so it's Catch-22. Has anyone ever run into this problem? What did you do?