From an AZ Republic article:

Closer to home, Isabel Garcia, a Tucson lawyer and chairwoman of Derechos Humanos, is also refusing to support the compromise agreement. She believes "thousands and thousands" of undocumented immigrants will be rounded up and deported before they get a chance to apply for legalization because the bill calls for a large increase in interior enforcement of immigration laws.

Many people who return to home countries to apply for permanent residency also will be barred from returning to the U.S. because they don't meet stringent requirements, she said.

"This is a program that is loaded with land mines," Garcia said.