The Lanham Act imposes on a trademark’s owner the requirement that the mark be used lawfully in commerce. If it is not, the USPTO should refuse to register it, and if registered the registration should be canceled. As well, unlawful use of a trademark in commerce has been applied as an affirmative defense to infringement in the case of registered marks, and there is no basis to distinguish, for this purpose, registered and unregistered marks. It’s just that the tested cases have been with registered marks.
Federal courts are prone to apply licensee estoppel to prevent a trademark licensee from challenging its prior licensor’s rights in the mark. If, of course, a licensee can establish that the prior licensor has no rights in the mark-at-issue, that licensor will not be able to enforce its rights in the mark. Those circumstances will often arise when the prior licensor sues it prior licensee because the latter continues to use the mark following expiration of the license.