Product label, as in its packaging? Or a stick-on label?
From Section 304 of the Tariff Act of 1930, as amended (19 U.S.C. 1304):
Part 134 of the CBP Regulations (19 CFR 134), implements the country of origin marking requirements and exceptions of 19 U.S.C. 1304. 19 CFR 134.43(a) requires that: Except for goods of a NAFTA country, articles of a class or kind listed below shall be marked legibly and conspicuously by die stamping, cast-in-the-mold lettering, etching (acid or electrolytic), engraving, or by means of metal plates which bear the prescribed marking and which are securely attached to the article in a conspicuous place by welding, screws, or rivets: knives, forks, steels, cleavers, clippers, shears, scissors, safety razors, blades for safety razors, surgical instruments, dental instruments, scientific and laboratory instruments, pliers, pincers, nippers and hinged hand tools for holding and splicing wire, vacuum containers, and parts of the above articles. Goods of a NAFTA country shall be marked by any reasonable method which is legible, conspicuous and permanent as otherwise provided in this part.
Further reading says that products that are easily separated from their packaging must be permanently marked