Supreme Court Reverses Coronado Decision, Opens Unions to Antitrust Liability

The Supreme Court unanimously reverses its 1922 Coronado decision, ruling that the United Mine Workers local union violated the Sherman Antitrust Act by conspiring to restrain interstate commerce in coal. After the Court’s first ruling favored the union by finding insufficient evidence of intent to affect interstate trade, Coronado Coal Company returned with an amended complaint demonstrating that union members refused to work on buildings constructed with non-union coal, which the Court now deems proof of conspiracy to suppress competition. Chief Justice William Howard Taft writes that when “intent to restrain trade” accompanies a decrease in production, a previously “indirect and remote obstruction” becomes direct interference violating antitrust law.

The decision opens floodgates for antitrust litigation against unions, with mine operators filing numerous copycat suits alleging the UMWA violated the Sherman Act by attempting to suppress competition from non-union coal. In subsequent years, the UMWA is named as defendant in more antitrust actions than any other union. More significantly, the Court’s sweeping reasoning casts doubt on the legality of virtually any strike that might reduce production or interstate commerce—an interpretation so broad it threatens to criminalize core labor organizing tactics. The ruling demonstrates how antitrust laws, originally designed to constrain corporate monopolies, are weaponized against workers’ collective action while corporations face minimal antitrust enforcement during the same period.

The Coronado reversal exemplifies the Supreme Court’s systematic hostility to organized labor during the 1920s, part of the broader Lochner Era pattern of invalidating worker protections while sanctioning corporate power. Justice Louis Brandeis and Oliver Wendell Holmes, who had dissented in other anti-labor cases, do not write separately here, suggesting even the Court’s more progressive members see the evidence of intent as sufficient under existing precedent. The decision stands until 1940, when the Supreme Court finally nullifies the Coronado doctrine. For 15 years, the ruling hangs over the labor movement like a sword of Damocles, enabling employers to threaten crippling antitrust judgments against any union that dares to organize aggressively or strike in ways that might affect interstate commerce.