As Apple Inc. (Nasdaq: AAPL) introduced the third version of its iPad tablet, activists in the United States renewed claims that the company's contract manufacturers in China exploit workers under what amount to slave-labor conditions.

Apple says it cares about its workers and requires its factories to follow the law, reads a petition that began circulating Wednesday from activist organizers SumOfUs. Well, we want to give Apple the chance to prove it.

The Washington, D.C., group issued its petition just as Apple was wrapping up the rollout of the new iPad in San Francisco. It called on the world's most valuable company to release workers' clock-in and clock-out times from the past four months at iPad-making factories in China.

Apple, based in Cupertino, Calif., no longer manufactures any of its products in the United States. It procures the iPad mainly from Taiwan's Hon Hai Precision Industry Co., part of Foxconn Technology Group. Hon Hai employs about 700,000 people in China, primarily in the southern mainland city of Shenzhen.

Apple also relies on components supplied by many other Asian manufacturers, notably Samsung Electronics Co. of South Korea.

Last month, just before its annual meeting in California, Apple said it had asked the Fair Labor Association, an industry-backed group, to audit its Chinese subcontractors' factories and report back.

That's not enough for SumOfUs, which describes itself as a movement of consumers, workers and shareholders speaking with one voice to counterbalance the growing power of large corporations. It alleges that Apple has broken Chinese laws on overtime pay in the past, citing reports by the New York Times that workers, among other things, were forced back to the assembly line when the late Apple co-founder Steve Jobs didn't like plastic screens in the iPhone and demanded glass instead.

The Apple contractors' employees were forced to put in 80 to 100 hours of overtime (on top of the 174 hours of regular work) each month, according to the petition on the group's website, SumOfUs.org.

The petition notes that Foxconn told the Times that it keeps computerized time cards for employees, making information about their hours easily accessible. The data should just be sitting there in a database already, it reads.

Also, SumOfUs writes, We hope as much as anyone that Apple has nothing to hide, but until the information is provided, customers and investors can only assume Apple is bluffing about caring about workers' health and safety.

Apple didn't respond to the SumOfUs petition, but Chief Executive Tim Cook said last month, We believe that workers everywhere have the right to a safe and fair work environment. When he hired the Fair Labor Association, Cook instructed the trade group to inspect plants in Shenzhen and Chengdu where there had been reports of worker suicides and other problems.

The company is also seeking inspections of factories owned by two other of its Taiwan-based vendors -- Quanta Computer Inc., which also supplies the Kindle tablet line to Amazon.com Inc., and Pegatron Technology.

Apple's board of directors, including former U.S. vice president Al Gore, was criticized for not seeking a labor-standards audit in the past. But the matter wasn't brought up at the company's annual meeting because Cook had already requested the audit  by the Fair Labor Association.

Analysts have said Apple, which announced the new iPad will sell for as much as $829, is so profitable that it could easily absorb higher pay for its subcontracted work force. The company's gross margin on all products was 44 percent in the first quarter ended Dec. 31, one of the highest of any electronics maker.

Dell Inc., the world's No. 3 PC maker, reported a 21 percent gross margin for its first quarter ended Feb. 2.

Apple shares rose Friday to $545.62, up $3.63, valuing the company at $508.6 billion. The stock's record high of $548.21 was set March 1. It has gained nearly 35 percent so far this year.

Taipei-traded shares of Hon Hai rose 0.5 percent Friday. They have gained about 22 percent in 2012.