There are various ways that violators can be punished, but there should be no abuse or violations of human rights. I will try to think of some reasonable and fair consequences for violators.

Deportation — The most obvious solution is deportation, but this must be considered in view of the particular consequences, such as whether or not the violator is escaping dangerous circumstances, or whether or not deportation will separate parents from children.

Prison — Probably not the best solution. Not only would the people of the United States have to pay (through income tax) for the cost of keeping people in prison, but life in prison might actually be better for the violator than their life before entering the U.S.

Fines — The violator could be charged with a reasonably large fine. They could stay in the U.S. but they would have to pay off the fine, probably over a period of several years, before they could be reclassified as a permanent resident. There would have to be some sort of background investigation to make sure that the violator has no criminal record, or is not a gang member, or involved with illegal drugs, or whatever, and anyone deemed undesirable would need to be deported.