Even if companies could not use illegal immigration in the workplace, there would still be immigrants trying to come to America. Besides jobs, immigrants come to America to have freedom. In America, immigrants can practice any religion that they want. They come to escape the poverty of their country and to give better opportunities to themselves and their family. Immigrants come to this country to try to live the American Dream, and even if illegal immigration in the work place were prevented, there would not be much change in the world.
The presence of immigrants actually adds about ten billion dollars to the US economy every year. Even without immigration, companies would want to find other ways to cut corners and make money. There would be a high demand for workers. Companies would still want underpaid workers and consumers would still want the cheapest prices on the goods they buy. In the end companies would just outsource more. Outsourcing would give companies access to a large pool of workers in another country. Companies would just create sweatshops and the workers would be underpaid, overworked, and abused. This would give the companies the cheap labor that they want and satisfy the consumer’s demand for cheap prices. Besides this, outsourcing does not require companies to pay for benefits, such as healthcare, giving the company an even bigger profit.
In conclusion, even without illegal immigrant labor, there would not be much change. There would be fewer jobs in America and more jobs overseas. Of course, this raises the following questions: What jobs can we not outsource? Why are we, America, okay with outsourcing, but not immigrant labor? Is there a way to prevent illegal immigration and sweatshop outsourcing, while still satisfying the needs above (many workers, cheap labor, and low consumer prices)?
Sources:
http://jobs.lovetoknow.com/Reasons_for_Outsourcing
http://www.squidoo.com/sweatshops
Arizona Immigration Laws 
Interesting perspective.
10.