This is very common problem and most common in countries where work visa is tied to a specific employers. The problem lies in the architecture of immigration laws and not providing freedom to join different employer, very easily with least beaurocracy, than the sponsoring employer. Law makers should understand that word "Temporary" more signifies the duration NOT the title of employer or establishment or Business. Work Visas should be duration oriented not employer oriented which means a 3 year work visa must allow worker to work for any employer in order to prevent him from discrimination rather than the one who filed his/her paperwork.
These abuses can only be stopped when freedom to join other employers is given to worker. In England, HSMP visa allows you to work for any employer, do any business within its validity period same should be in all temporary work visa programs. When you tie one employee to a specific employer that's when all exploitation starts. In United States, H1B Visa has a little room to change employer which allows many candidate to protect themselves from exploitation. The fear of deportation always will be in mind of an immigrant when he will be tied to one specific employer and it is a common thing all across the world. Low wages, High amount of work, abuse, discrimination are the common issues because of this architecture of law.
