In the 1977 case of New Hampshire v. Maine, the U.S. Supreme Court was asked to resolve a boundary dispute between the two states over their shared border along the Piscataqua River. The disagreement centered on whether a 1740 decree by King George II of England that established New Hampshire's eastern boundary should be interpreted as placing all islands and waters in Portsmouth Harbor within Maine's jurisdiction or if it allowed for some areas to fall under New Hampshire’s control. The court ruled in favor of Maine, citing principles from international law regarding river boundaries and historical evidence showing that both states had long accepted this interpretation of their shared border. Furthermore, they applied judicial estoppel preventing New Hampshire from arguing against an agreement it made with Maine in previous litigation about lobster fishing rights where they acknowledged those territories belonged to Maine.

In the dissenting opinion for New Hampshire v. Maine, 1977, Justice William Rehnquist disagreed with the majority's decision to apply judicial estoppel against New Hampshire. He argued that this doctrine should not be used in a case involving two sovereign states over a boundary dispute because it was not an ordinary civil litigation between private parties where one party might gain an unfair advantage by playing fast and loose with courts. Instead, he believed that such disputes should be resolved based on historical evidence and legal principles rather than procedural doctrines like judicial estoppel which could potentially lead to unjust results. Furthermore, he pointed out that there were significant differences between the present case and previous cases where judicial estoppel had been applied as those involved attempts by litigants to contradict their own sworn statements made in earlier proceedings while no such contradiction existed here.