Former employer withholding check, question about notifying ex boss?

It's not retaliation to file a claim with the department of labor. I would do so ASAP. It's up to her to prove that the shirts are company property and need to be returned. Either way, it's unlawful for her to hold up your check for any reason. You have the right code already. I'd go after her for the 8% interest that's now owed to you for their failure to get the check to you on time, under the terms of the law.