From the FTC website:
Threading Your Way Through the Labeling Requirements Under the Textile and Wool Acts
The label(s) with required information must be securely attached to the product until it is delivered to the consumer. However, the label(s) need not be permanently attached.
Note: Many consumers and professional cleaners consider it important to have fiber information on a permanent label. Also, remember that garments must have care instructions on a permanent label. Therefore, it may be useful to have the two pieces of information on the same label.
Note: Customs may require that the country of origin of imported goods be on a sewn-in label.