Republican Meg Whitman has forcefully denied that she knew her former housekeeper was in the country illegally, keeping immigration in the spotlight in California's gubernatorial race.

Q: What are people required to do to verify the immigration status of household workers, such as cleaners, gardeners, painters and carpenters?

A: In general, employers must fill out and sign the U.S. Citizenship and Immigration Services' I-9 form, which requires them to acknowledge, under penalty of perjury, that they examined documents that entitle an employee to work. However, the form is not required for "casual domestic work in a private home on a sporadic, irregular or intermittent basis," according to CIS' employers guide.

Dan Kowalski, editor of Bender's Immigration Bulletin, said "sporadic" work has not been clearly defined by case law, making it open to interpretation. A full-time nanny's employer, he says, would be required to fill out an I-9 form.

Independent contractors are also exempt. Kowalski says the term "independent contractor" is well-defined by case law; the person hired to paint a living room is not required to fill out an I-9.

Q: Is an employer shielded from legal trouble if the worker is contracted by an agency?

A: Yes. But Kowalski says that means the employment agency pays the worker. If Whitman paid the worker directly, she became the employer and should have signed the I-9 form, he says.

Q: What if the employer suspects a worker is using false documents or someone else's documents?

A: CIS says an employer must reject documents that "do not reasonably on their face appear to be genuine and to relate to the person presenting them." It sponsors a voluntary program that lets employers run a worker's information against Department of Homeland Security and Social Security databases. More than 216,000 employers were enrolled in the E-Verify program through September 2009.

I-9 forms are not submitted to the government, but an employer must keep them for three years after the hiring date or a year after the date of termination, whichever is later.

For more information, see CIS' employers guide, http://www.uscis.gov/files/nativedocuments/m-274.pdf