From Nat’l Ass’n of Hom Builders v. OSHA, 602 F.3d 464 (D.C. Cir. 2010):

A driver exceeding the speed limit runs a red light and swerves onto the opposite lane. Three violations of the law against reckless driving or one? Five punches to a victim's face without provocation. One battery or five? Same result if the punches were hours apart? The financial officer of a corporation with 10,000 shareholders submits a false report to the Securities and Exchange Commission. One fraud or 10,000? These "unit-of-prosecution" questions have vexed state and federal courts. The questions are important. Prosecutors know that multiple charges encourage plea agreements and convictions. Defense attorneys know that it is easier to defend against one charge than many. Most people know that multiple offenses can result in multiple punishments.

Similar problems have dogged civil enforcement proceedings. See, e.g., Missouri, Kansas & Texas Ry. Co. v. United States, 231 U.S. 112, 34 S. Ct. 26, 58 L. Ed. 144 (1913) (Holmes, J.). In this case, the Secretary of Labor amended rules under the Occupational Safety and Health Act to clarify that an employer's failure to provide respirators or workplace training constitutes not one violation of the applicable health and safety standards, but separate violations for each employee who did not receive the respirator or training. *** Three trade associations whose members are subject to these amended rules claim the Secretary had no statutory authority to issue the amendments. ***

Petitioners have one basic argument, which they repeat in many different forms. The argument is that under the Act, the Secretary had no authority to specify units of prosecution because Congress assigned such determinations to the Commission. We think there is nothing to the argument. ***

Petitioners fail to recognize that to define the violation is to define the unit of prosecution. In the criminal law this basic proposition has long been established. See, e.g., Crepps v. Durden, (1777) 98 Eng. Rep. 1283, 1288 (K.B.) (Mansfield, J.); In re Snow, 120 U.S. 274, 281-85, 7 S. Ct. 556, 30 L. Ed. 658 (1887). The responsibility for specifying the unit of prosecution is therefore the legislature's, not the judiciary's. See, e.g., Badders v. United States, 240 U.S. 391, 394, 36 S. Ct. 367, 60 L. Ed. 706 (1916); In re Snow, 120 U.S. at 281-82. The same is true in civil enforcement actions. As Justice Holmes wrote in a civil case raising a unit-of-prosecution issue, "the real question is simply what the statute means." Missouri, Kansas & Texas Ry., 231 U.S. at 119. Here we are concerned not with statutory violations, but violations of the Secretary's standards. In that respect, the Secretary stands in the shoes of the legislature. And so petitioners' argument evaporates. In giving the Secretary the authority to define what constitutes a violation, *** the Act necessarily gave the Secretary the authority to define the unit of prosecution.

Petitioners insist that the Commission alone has the responsibility to determine units of prosecution because, under 29 U.S.C. § 666(j), the assessment of penalties is the Commission's exclusive domain. This is like saying that in a criminal case the court — not the legislature — defines the unit of prosecution because the court has exclusive authority to determine the punishment. That of course is not the law. See, e.g., Sanabria v. United States, 437 U.S. 54, 69-70, 98 S. Ct. 2170, 57 L. Ed. 2d 43 (1978); Bell v. United States, 349 U.S. 81, 82-83, 75 S. Ct. 620, 99 L. Ed. 905 (1955); United States v. Anderson, 509 F.2d 312, 332, 165 U.S. App. D.C. 390 (D.C. Cir. 1974).