During his time on the court, Pitney developed a relatively conservative reputation and was an adherent of the judicial philosophy of substantive due process. This belief was exemplified in his majority opinion in "Coppage v. Kansas", where, in ruling unconstitutional a Kansas statute banning anti-union yellow-dog contracts, the court stated that police power could not be legitimately utilized to ensure equality of bargaining power. Although distrustful of unions, Pitney also feared the rampant expansion of business and supported a broader use of the Sherman Antitrust Act.