Roughly $150 billion is sent abroad every year to the family, friends and business associates of people living in this country illegally. These individuals often do not pay an income tax, and when that money is spent in the country it was sent to, the consumption taxes, sales taxes, etc, will not contribute to the local, state or federal tax revenues in the United States. Nevertheless, illegal migrants have the ability to utilize or consume any publicly funded benefits that do not require a valid social security number to access.
Therefore, money that is sent overseas should be taxed, from anywhere between 10% to 30%. A lower percentage tax would serve to fund the bare minimum to offset what illegal migrants utilize and consume while living in here. A higher percentage tax can act as a deterrent, discouraging people from illegally migrating in the first place. To limit this tax so that it only applies to illegal immigrants, a federal income tax break could be given.
Vice President-Elect, JD Vance, has supported similar legislation in the past.
Here is an excellent webpage from FAIR, the Federation for American Immigration Reform, detailing the facts about remittances, much more thoroughly than I can
https://www.fairus.org/issue/united-states-loses-150-billion-annually-remittances/