>[The Congress shall have Power] To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes
4th amendment
>The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
Basically, when you engage in commerce, your rights to be secure and have privacy in personal matters is diminished because you've entered into a public sphere interacting with others with money.
Law gets to reach in and have influence in how people exchange money and goods, but not into their personal affairs. There are graduated levels of "this is my business" vs. "laws can be made about this behavior" depending on the activity.