Protestors stand outside Apple's developers conference. (Courtesy of SEIU-United Service Workers West)

Thousands of developers streamed into a San Francisco convention center Monday to see Apple chief executive Tim Cook speak about the company's future  during its Worldwide Developers Conference. But just outside the doors to the Moscone Center there was a much different kind of queue to contend with -- a picket line.

Around 20 demonstrators from a local union took up posts outside the building ahead of Cook's Monday morning speech, chanting and passing out flyers claiming that Apple is hurting its local community by not paying its fair share of state taxes.

The tax issue is not a new one -- in fact the protesters echoed concerns raised by Congress that Apple and other tech firms were using tricks to avoid corporate federal taxes. But the question of how much Apple or other firms pay in taxes has become one of several beefs that San Francisco activists have leveled at California's technology industry. Tensions between the two have simmered for months in the state, as a growing number of local activists say that the country's most successful companies aren't doing their part to improve the communities around them.

Apple has denied claims that it's using loopholes to pay less than its fair share. Cook himself told lawmakers at a Congressional hearing last year that Apple pays every dollar that it owes in taxes and doesn't rely on "tax gimmicks."

But local activists such as those who protested Monday say that if that were the case, the Bay Area would have flourished along with those companies.

"When people talk about Silicon Valley, San Francisco or this whole area, people think that because it's the home of all this big tech that everything should be fine," said Sam Kehinde, who organized the protest as part of a larger campaign targeted at major tech companies. "There should be good roads, infrastructure and good-paying jobs. But that's not the case. Big tech has beautiful campuses, beautiful offices. But the general public's community suffers."

The problem isn't exclusive to Apple, said Alfredo Fletes, a spokesman for the SEIU-USWW, the union that organized the protests and represents security workers who have worked as contractors for major tech firms. But, Fletes said, he believes that Apple should use its position as a leader in the technology community to set best practices.

Kehinde, a former security worker, has campaigned against Apple and Google in the past over the companies' decisions to work with a firm that he says doesn't pay security officers fairly. He and other protesters brought their concerns to Apple in 2012 at the company's shareholder meeting. Apple and the SEIU have since both spoken to an intermediary about the problem, Kehinde said, but have been unable to resolve the conflict. And so the demonstrations continue.

Apple declined to comment on the protest. The contracting firm, SIS, has denied the labor accusations and said the protests are an attempt to pressure its workers into unionizing.

Kehinde, who is planning a similar protest at Google's developers conference later this month, said that his goal is not to take down these tech firms or cast them as villains.

"We want to sit down with them and talk about how to make this work for everyone," he said. "We all love Apple products; we all pick them up. It's up to them to pick up the community where they design these products."