Because it's amnesty

Hayworth Says Congress Needs Help Halting Bush's Guest-Worker Plan
With the Senate about to finally address immigration reform and President Bush renewing his call for a guest-worker program in last week’s State of the Union, Rep. J.D. Hayworth (R.-Ariz.) tells HUMAN EVENTS he foresees a troubling scenario that will result in an amnesty plan being “shoved down the throats” of the American people.

...if people do not obey existing laws, and if the government refuses to enforce existing laws, what makes us think any new laws are going to be either enforced or obeyed?

The United States Chamber of Commerce, the agri-jobs group, the service industries are just bound and determined that they want to have what is in effect corporate welfare—a permanent subsidy to absorb their costs of doing business by bringing people in and creating a new status of worker that essentially would be paid for by the taxpayers of the United States to facilitate a new American caste system or a permanent underclass.

Just go read this whole interview with Rep. J.D. Hayworth.