Please answer a question about the following article about Clothing:

Though mechanization transformed most aspects of human industry by the mid-20th century, garment workers have continued to labor under challenging conditions that demand repetitive manual labor. Mass-produced clothing is often made in what are considered by some to be sweatshops, typified by long work hours, lack of benefits, and lack of worker representation. While most examples of such conditions are found in developing countries, clothes made in industrialized nations may also be manufactured similarly, often staffed by undocumented immigrants.[citation needed]

What type of immigrant often staff sweatshops?
undocumented