For more than a decade after its passage,
the Sherman Act was invoked only rarely
against industrial monopolies, and then not
successfully, chiefly because of narrow
judicial interpretations of what constitutes
trade or commerce among states. When it
was first passed, the Sherman Antitrust Act
was largely ineffective at stopping
industrial monopolies. Courts at the time
tended to hold a very narrow view of what
constituted "trade or commerce among
states," and most companies were not held
liable under the act. For more than a
decade after its passage, the Sherman
Antitrust Act was invoked only rarely
against industrial monopolies, and then not
successfully. Ironically, its only effective
use for a number of years was against
labor unions, which were held by the courts
to be illegal combinations.