Some unethical businesses are eager for migrants to come here so they fill vacancies because they are not prepared to act within the local/national market and allow it to set conditions and wages; but prefer to do the dirty on the taxpayer by shortcutting the market with immigrant low wage labour thus keeping native citizens unemployed and on welfare, paid bythe taxpayer, whist the job is underpaid (and might even attract more welfare to top it up, again from the taxpayer).
Allowing it to happen is not the way to deal with it. Minimum wage for a full time job should never be so low as the employee needs to get welfare on top; and there should be clear indication of conditions and wages being reasonable, and long attempts at getting native employees first, before being allowed to apply for immigrants to enter and take up job positions here.