In the Southern Union Co. v. United States case, the Supreme Court ruled that any fact leading to a criminal fine must be proved beyond reasonable doubt or admitted by the defendant. The energy company, Southern Union, was convicted of storing liquid mercury without a permit and fined $38 million based on how many days it had been in violation of this law - an amount determined by the judge rather than a jury. The court held that this violated Southern Union's Sixth Amendment rights because it increased their penalties beyond what was found by a jury or admitted by them during plea bargaining. This ruling extended Apprendi v New Jersey (2000), which stated that any fact increasing maximum prison sentences must be decided upon by juries using 'beyond reasonable doubt' standards.

In the dissenting opinion for Southern Union Co. v. United States, Justice Breyer, joined by Justices Kennedy and Alito, argued that the majority's decision to apply Apprendi to fines was unnecessary and could potentially disrupt a significant amount of federal sentencing practice. They contended that there is no historical evidence supporting the application of jury trial rights to criminal fines as they were traditionally imposed by judges in England and early America without juries' involvement. The dissent also pointed out practical difficulties with requiring juries to determine fine amounts or set upper limits on them given their lack of expertise in assessing complex financial information often involved in such cases. Furthermore, they expressed concern about potential negative impacts on plea bargaining since defendants might be less willing to plead guilty if they knew a jury would decide their fine rather than a judge who might be more lenient.