Key parts of Georgia's new law targeting illegal immigration are set to take effect next week, adding exhaustive proofing methods to Georgia businesses and government services meant to reduce the number of illegal immigrants who work in the state or receive its benefits.

Starting Jan. 1, any employer with 500 or more employees will have to use a federal database called E-Verify to check the employment eligibility of all new hires.

The mandate is being phased in with smaller businesses that have 100 or more employees starting July 1, and companies with more than 10 employees starting to use E-Verify by July 2013. Employers with 10 or fewer employees are exempt.

The law's sponsor and supporters said they wanted to deter illegal immigrants from coming to Georgia by making it tougher for them to work in the state.

Already, any company with a federal contract is required to use E-Verify, and Georgia has required state and local government agencies and their contractors to use the database since 2007.

But the new law could cause trouble for many businesses, experts say.

"Many Georgia businesses are confused with respect to the provisions of the law that have to do with E-Verify," said Atlanta lawyer Teri A. Simmons, who advises businesses on immigration and employment matters. "Within most businesses, human resources professionals are already dealing with so much that it's hard to also fit in E-Verify training and administration."

Local government officials have already complained about the amount of work the bill creates for officials in charge of handing out business licenses.

Also taking effect Jan. 1 is a provision that any agency administering public benefits — including business licenses — must require each applicant to provide at least one "secure and verifiable document." A list of acceptable documents was provided by the attorney general's office over the summer.

But municipal officials have complained of what they say are unintended consequences of the bill that create more work for local governments that are already lean on staff.

Local governments around the state could face penalties for not properly enforcing the law, but a letter from Attorney General Sam Olens to the bill's chief author states that the law is ambiguous when it comes to what precautions local governments should take to make sure no illegal immigrants are hired or receive a public benefit.

When Gov. Nathan Deal signed the law in May, Georgia joined Arizona and several other states that have recently enacted tough laws taking aim at illegal immigration. Federal judges have since blocked all or parts of the various laws, and Arizona's is headed to the U.S. Supreme Court next year.

The new law also instructs the state agriculture department to submit a report to the governor and the heads of each chamber of the state legislature by Jan. 1.

The department was tasked with examining the effect of immigration on the state's agriculture industry and providing suggestions to reform a federal guest worker program. The department also was supposed to evaluate the feasibility of a state guest worker program.

Associated Press contributed to this report.