Low wages aren’t illegal. Their point, which is valid whether you accept it or not, is that an increase in available labour drives down the cost of that labour. Why use a uk plasterer charging a premium when you have access to a hundred more who are happy to send a minimum wage back to their families in the eastern bloc?

People face loss of job security, and a highly diversified work force is less likely to unionize. Workers have everything to fear from foreign labour.

The solution of course is to give every migrant worker legal status so that they can't work less than minimum wage, but a) that will never fly here, and b) that only puts a cap on how low wages can go, without any path to raising them