In the case of Clayton Mark & Co. et al. v. Federal Trade Commission, the Supreme Court ruled in favor of the Federal Trade Commission (FTC). The dispute centered around whether Clayton Mark & Company's exclusive dealing contracts violated Section 3 of the Clayton Act, which prohibits certain business practices that may harm competition or create a monopoly. The FTC argued that these contracts did indeed violate this section and issued a cease-and-desist order to prevent further use of such agreements by Clayton Mark & Co., who then appealed to have this order set aside. The Supreme Court upheld the FTC's decision, asserting that it was within its rights to issue such an order if it believed there was reasonable probability that these contracts could suppress competition in a substantial share of line pipe market - even if no actual harm had yet occurred as per their interpretation under Section 5 (unfair methods) rather than Section 2 (monopolization) or Section 7 (mergers/acquisitions). This ruling reinforced FTC’s authority over potential anti-competitive behavior before any damage is done.

In the dissenting opinion for Clayton Mark & Co. v. Federal Trade Commission, Justice Jackson disagreed with the majority's decision that Clayton Mark & Co.'s exclusive dealing arrangements violated Section 3 of the Clayton Act. He argued that there was no evidence to suggest these agreements substantially lessened competition or created a monopoly in any line of commerce. The dissent emphasized that it is not enough to simply show an agreement exists; rather, it must be demonstrated how such an agreement leads to anti-competitive effects within a relevant market area. Furthermore, he pointed out inconsistencies in applying this standard across different cases and warned against overreaching interpretations of antitrust laws which could stifle legitimate business practices and innovation.