Amicus curiae, or "friend of the court", briefs offer non-parties to a case an opportunity to address the effect of a decision on their interests. Such a brief can alert the court to those effects when they are not addressed by one of the parties. Price v. New York City Board of Education, 837 N.Y.S. 2d 507, 516 (N.Y. Sup. 2007). It can do so by presenting "ideas, arguments, theories, insights, facts, or data that are not to be found in the parties' briefs." Voices for Choices v. Illinois Bell Telephone Co., 339 F. 3d 542, 545 (7th Cir. 2003). Conversely, it should not cover the same ground that the party it supports has covered or encourage the court to consider the identity of the parties or their amici ahead of the facts and the law in deciding the case.

In Coca-Cola Bottling Co. v. Harmar Bottling Co., 218 S.W. 3d 671 (Tex. 2006), the Supreme Court of Texas considered whether so-called calendar marketing agreements entered into between Coca-Cola bottlers and local retailers violated the Texas Free Enterprise and Antitrust Act of 1983. The court also considered whether that Texas state law could be applied extraterritorially to provide a remedy for antitrust injuries to competitors of the Coca-Cola bottlers whose territories lay in Arkansas and Oklahoma. At the merits stage, the State of Alabama, under Attorney General Troy King, submitted an amicus brief in which it observed that the antitrust laws of the several States differed and contended that the application of the Texas law, the injunctive powers of the Texas courts, or both to injuries to consumers outside Texas from competitive practices outside Texas violated the interests of interstate comity. The State of Alabama noted that one of its corporate citizens, a Coca-Cola bottler which did not operate in Texas and whose territory included Tennessee, Georgia, South Carolina, Alabama, Mississippi, and portions of Louisiana, might be subject to suit in Texas for the same competitive practice. Alabama explained that it had "no problem with Texas' redressing injuries incurred in Texas that result from conduct outside that State if that is what Texas law provides. The Texas courts should refrain, however, from redressing injuries to citizens in other States that are independent of any injuries in Texas. Interstate comity, supported by considerations of international comity, favors restraint."

In October 2006, the Supreme Court of Texas reversed the judgment against the Coca-Cola entities, holding that the Texas antitrust law did not apply extraterritorially, and that the trial court should not have considered the claims under the laws of Arkansas, Louisiana, and Oklahoma. The non-Coca-Cola bottlers asked for rehearing, and the States of Arkansas and Oklahoma each supported them with amicus submissions by their respective Attorneys General. Both States suggested that an appropriate way of determining how the antitrust laws of their States applied to calendar marketing agreements, which are not generally viewed as per se illegal but have not been addressed in the Arkansas or Oklahoma courts, would be to certify questions to their Supreme Courts. The Attorney General of Arkansas, Dustin McDaniel, also suggested that, if the Texas courts got its antitrust law wrong, Arkansas could fix the error when an attempt to domesticate the Texas judgment in Arkansas was made. The Attorney General of Oklahoma, W. A. Drew Edmondson, also questioned Alabama's interest in the case, and argued that it was inefficient to expect the plaintiffs to file suit in Oklahoma, Texas, and Arkansas to obtain relief.

Alabama and others responded to these submissions. Alabama noted that the Full Faith and Credit Clause of the United States Constitution allows for only "a few, relatively narrow policy based exceptions to the states' obligations to enforce the judgments of other states' courts." Erin O'Hara, "Full Faith and Credit Clause" in Meese, Spalding, Forte, eds., The Heritage Guide to the Constitution (2005). According to Alabama, Arkansas' suggestion that it could revisit the judgment of a Texas court to make sure that Texas got the Arkansas law right does not fit into any of those exceptions. Certification also appeared unworkable in that an entire trial record was at issue. Would the Supreme Court of Oklahoma or Arkansas have to review the whole record to decide whether the competitive practices of the Coca-Cola entities in their States violated their antitrust laws? Finally, according to Alabama, separate lawsuits in the several States might not be efficient, but efficiency does not trump jurisdictional limitations, and federal court was available.

On May 4, 2007, the Supreme Court of Texas denied rehearing.

Harmar is not the first time that state Attorneys General have disagreed in their amicus submissions, and it will not be the last. What may be more important than the disagreement is the interest supported. In Harmar, Alabama spoke for one of its corporate citizens and advanced the interest of interstate comity, an interest that the Supreme Court of Texas endorsed. The Attorneys General of Oklahoma and Arkansas claimed to protect the interests of their citizens by suggesting that the Texas courts could protect them. Critics of their position would argue that the courts of Oklahoma and Arkansas are to serve this purpose.