Proposition 202 gets to the "heart" of the illegal immigration problem by cracking down on the underground economy based on employers who pay their workers off the books, said Garrick Taylor, a spokesman for Stop Illegal Hiring.

"We're talking about eliminating the environment where illegal hiring has been allowed to fester and that is in the black-market economy," Taylor said.

By not allowing anonymous complaints, Proposition 202 protects employers from competitors and disgruntled former employees, he said.

Jim Klinker, the chief administrative officer of the Arizona Farm Bureau, said there are concerns with the accuracy of the E-Verify system, which federally is a voluntary program. It's also only used after a company has hired an employee, he said. For that reason, Klinker said, changes should be made to the federal requirements.

Republican activist Don Goldwater called Proposition 202 "employer amnesty."

Goldwater said E-Verify has been an effective tool in determining whether a person can work in the United States legally, and Proposition 202 would remove that component from Arizona law.

Allowing employers to use the federal guidelines for verification means the fraudulent business practices employers have used in the past will continue, said Tim Rafferty, who sits on the board of directors of Riders United for a Sovereign America, or RidersUSA.

Also, while law enforcement has often relied on anonymous tipsters to receive reports of illegal activity, Proposition 202 would take away that ability, Rafferty said.