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Meg Whitman's campaign for governor was thrown into turmoil Thursday as the Republican sought to fend off new evidence that she knowingly had an illegal immigrant housekeeper on her payroll for nearly a decade.

Whitman denounced the allegations as a "baseless smear attack" by Democratic challenger Jerry Brown in what has become a dead-heat race five weeks before the election. She says she fired the $23-an-hour housekeeper last year immediately after learning she was illegal.

The immigration dispute has upended a contest that until now been focused on serious issues such as job creation, state spending and education in a state with a $19 billion deficit and 12.4 percent unemployment.

Now, the focus is on whether the billionaire GOP nominee for governor will take a polygraph test to respond to allegations brought by a celebrity-seeking attorney and her mysterious housekeeper client.

Revelations about the illegal housekeeper have also thrown Whitman's carefully managed campaign completely off track and opened the door for Democrats to accuse her of hypocrisy.

The former eBay chief executive has called for tougher sanctions against employers who hire illegal workers, and the fact that she employed an illegal immigrant maid from Mexico for nine years could undermine her credibility. She has also spent millions courting Latino voters, who could play a key role in determining the outcome of the race.

A letter sent to Whitman from the Social Security Administration in 2003 has emerged as a crucial element in the dispute. The letter warned Whitman that there were discrepancies in housekeeper Nicky Diaz Santillan's payroll documents, a possible tip-off that she could be illegal.

Whitman said she never got the letter and suggested the former maid might have intercepted it since she was in charge of the mail at the family's Silicon Valley mansion.

The housekeeper and lawyer Gloria Allred later produced a copy of the letter that they say shows Whitman's husband, Dr. Griffith Harsh III, partially filled it out and told the housekeeper to "check on this."

Allred said the housekeeper recognized the writing as belonging to Whitman's husband, and a handwriting specialist may be brought in to analyze her husband's penmanship. She claims it could prove that Whitman and her husband knew years earlier that Diaz Santillan might be illegal.

In a statement released by the campaign, Harsh said he did not recall receiving the letter, although it's possible he scratched out the note asking Diaz Santillan to follow-up. He noted, however, that the letter does not say Diaz Santillan is illegal, it merely asks for more information.

"The essential fact remains the same, neither Meg nor I believed there was a problem with Nicky's legal status," the husband said. "The facts of this matter are very clear: Ms. Diaz broke the law and lied to us and to the employment agency."

The story has consumed the two full days of news cycles just as Whitman and Brown are preparing for a Saturday Spanish-language debate that will include questions of importance to the Hispanic community.

One of the state's largest public employee unions immediately released a Spanish-language attack ad accusing Whitman of a double standard on illegal immigration.

Whitman, who has revealed few details about her personal life since announcing her first run for office last year, was forced to spend 45 minutes answering questions from reporters about what she knew and when she knew it, her husband standing awkwardly by throughout.

"You know, I've only been in politics for two years. I'm just getting used to the smear politics, I'm just getting used to the politics of personal destruction," she told dozens of reporters hastily gathered at a hotel in Santa Monica.

Whitman has spent a record $119 million of her own money on the race, and her campaign has been marked by its uncanny ability to stay on message. That marks a notable contrast with Brown, the state's attorney general and a former governor known for talking off-the-cuff, sometimes too much.

The timing of the allegations so close to the Spanish-speaking debate, the lack of extensive documentation, and Allred's Democratic ties left her open to questions about motive. Allred once gave money to Brown, and she was a Hillary Rodham Clinton delegate at the Democratic National Convention in 2008.

Allred, who is well-known for orchestrating media stunts, has not permitted Diaz Santillan to answer a single question from reporters over two days of news conferences. The former housekeeper read a brief, prepared statement Wednesday that alleged brusque treatment during her nine-year tenure. Whitman said it was "not the Nicky I know."

Allred said Thursday she is not providing any financial support to her client and added her involvement with Diaz Santillan started "within the last week."

Two days after she made the allegations that reordered the race for governor, Diaz Santillan remains a mystery. Virtually nothing is known about her activities or whereabouts from the time Whitman fired her in June 2009 until she appeared Wednesday with Allred at her Los Angeles law office.

Whitman was repeatedly asked why she didn't just own up to this huge political liability earlier to avoid a late election-cycle surprise such as this, particularly since she has repeatedly stressed the need to hold employers accountable for hiring illegal workers.

She said she didn't want to subject Diaz Santillan to the scrutiny -- and left unsaid, deportation -- that could have resulted from her reporting it. Whitman also noted that in California, employers bear no responsibility to report illegal worker, only to not knowingly hire and employ them.

"Because Nicky had worked for us for 10 years, I was very fond of Nicky and I didn't want to make an example of her. It's not an obligation of the employer to turn in illegal employees," she said.

The revelations come suspiciously close to Saturday's Fresno debate, which will air statewide on Spanish-language television in an effort by both camps to target one of the most highly sought-after voting blocs in the state. Hispanics are projected to comprise just 15 percent of voters in the Nov. 2 general election, but both sides have aggressively targeted them as potential swing votes.

Brown's spokesman, Sterling Clifford, said in a statement that Whitman apparently thinks the rules don't apply to her.

"After more than a year of Whitman demanding immigration policy that 'holds employers accountable,' we learn that accountability doesn't extend to her own actions," he said.

Clifford said the Browns use a well-known national housekeeping service that comes twice a month to their home in the Oakland Hills. He said Brown has never knowingly employed an illegal immigrant.