They're doing it with people Fiorina laid off at HP and by posting a cutting video on the Internet.
The video is supplied by /*Brave New Films*/, a production company that in the past has targeted Republican John McCain, as well as retail giant Walmart.
Fiorina, who got millions from HP when she was fired, laid off more than 30,000 people.
Fiorina and the layoffs were the targets at the /*Los Angeles County Federation of Labor*/, which has endorsed Boxer.
Two of the people fired by Fiorina were in attendance at a news conference held by Boxer supporters.
Susan Walsh was an executive administrative assistant at HP.
"I'm one of 30,000 and I'm struggling, and I'm on unemployment," Wash said. "And let me tell you, it's not pretty in my household."
Mike Angles was a manager with 21 years at HP. He was within 18 months of retirement.
"I'm really frightened by the potential damage that she can do in the future," Angles said. "But not at a company level -- now at a national level."
Before campaigning in Northern California on Tuesday, Fiorina was in Orange County on Monday and was asked about laying off all those people. She turned the subject to her opponent.
"What she has done is profited from her office and hurled political slogans, but she has not accomplished anything on behalf of the people of California," Fiorina said.
The head of the Los Angeles Federation of Labor, Maria Elena Durazo, said Fiorina was rewarded with a severance package worth millions of dollars.
"What were Susan and Mike and their colleagues rewarded with? Their jobs were shipped to China," Durazo said.
Outside the news conference, a former HP worker, defended Fiorina. Larry LaRock says he was laid off, but respects Fiorina.
"To be competitive. We were simply not competitive," Larry LaRock said. "We had to reduce costs at that point in time. And the only way you could do that is by reducing your workforce in the areas that you're not competitive in anymore."
Business groups and social conservatives have spent about $4 million on ads and other activities to help Fiorina.
In contrast, outside groups have spent about $121,000 helping Boxer. That money is spent independent of the campaigns.