Personally I know cases where immigrants hesitated to ask for standard market salaries.

Migrant workers typically take the low paid and low skilled jobs because it is still better money than they were getting at home.  Unfortunately language barriers and lack of awareness about rights means that they are a group that is especially vulnerable to exploitation, often not being paid the minimum wage and working long hours under terrible conditions - this is largely because they are being threatened with dismissal if they don't agree to this and they cannot afford it - especially if their accommodation is tied in with the job.

The vulnerable workers group also overwhelmingly includes women who get placed in the same situation and not knowing their rights, they put up with terrible conditions and pay because they can't afford to complain and lose their jobs.

See the Vulnerable Workers Report for more.