The right to engage in criticism as a form of free expression is generally not barred by trademark laws. However, the extent of this freedom likely varies depending upon territorial laws. Many countries have looked to the United States for legal guidance on this, which attributes trademark criticism to fair use. Lanham Act (Pub.L. 79–489, 60 Stat. 427, enacted July 5, 1946, codified at 15 U.S.C. § 1051 et seq. (15 U.S.C. ch. 22), section 1125. A more significant problem is when trademark criticism leads to trademark dilution or trademark confusion as a consequence of the criticism. Under these circumstances, the trademark owner may have legal recourse regarding trademark infringement.

Still, the trademark owner would have to prove that his/her brand (trademark) was damaged (diluted) as a result of the criticism. Moseley v. V Secret Catalogue, Inc., 537 U.S. 418 (2003). The Lanham Act § 43c(3)(B) and the Federal Trademark Dilution Act do not consider non-commercial criticism as trademark dilution. Case law concurs that non-commercial use of a trademark such as that of critical speech does not dilute the trademark. Bolger v. Youngs Drug Products Corp., 463 U.S. 60, 66 (1983).
Nominative fair use is a defense to trademark dilution considered by the Ninth Circuit Court of Appeals in the United States. This means that during the course of criticism, the critic deemed it necessary to use the trademark during the course of the discussion. Three criteria are used to determine behavior that constitutes nominative fair use: (1) the disputed product cannot be identifiable without trademark use; (2) the user must utilize only enough of the product to make criticism or commentary clear; (3) product endorsement or sponsorship is not allowed.
The trademark owner can sue, but it is not likely that he/she will prevail in a claim of trademark infringement due to critical commentary. BidZirk, LLC v. Smith, 2007 WL 3119445 (D.S.C. Oct. 22, 2007) (in which a blogger published criticism concerning an online retailer). The third circuit uses similar criteria (prongs one (1) and two (2)) for determination of nominative fair use. Yet, prong three (3) of the third circuit’s test questions the verity of the claims in the criticism (whether the claims are true or false). Century 21 Real Estate Corp. v. LendingTree, Inc., 425 F.3d 211 (3d Cir. 2005). Thus, a trademark owner may be held liable for making false claims.