These are usually illegal immigrants, without the legal right to work in the country. They're frequently severely underpaid, and without the legal rights granted to legal workers. Ironically, many of them emigrated from their home countries to avoid poverty.

The large number of illegal workers has created a series of major problems in employment in the US and elsewhere. Illegal workers often supply the workforce in jobs like agriculture and unskilled labor. Current figures indicate millions of illegal workers are working across a range of industries.