Apple’s labor practices are under attack by two activist groups who contend the company makes its iPhones with a hazardous mix of chemicals that threaten the health of factory workers assembling the devices in China.

The campaign began Wednesday with an online petition put together by China Labor Watch, a longtime Apple critic, and Green America, an environmental protection group.

If enough consumers sign the “Bad Apple” petition, the two groups hope to pressure the company into abandoning the use of two chemicals, benzene and n-hexane, in the production of the iPhone, Apple’s top-selling product.

Benzene is a carcinogen that can cause leukemia if not handled properly and n-hexane has been linked to nerve damage.

In a statement, Apple pointed out that it has already stopped using many hazardous chemicals, including PVC plastic and brominated flame, during the past few years to the acclaim of environmental groups such as Greenpeace. The Cupertino, Calif. company also says it ensures all remaining toxic substances comply with U.S. safety standards.

“Last year, we conducted nearly 200 factory inspections which focused on hazardous chemicals, to make sure those facilities meet our strict standards,” Apple said.

The protesting groups believe Apple’s factory inspections and publicly released reports about the findings have been whitewashing the real working conditions. They say they suspect many of the estimated 1.5 million workers in overseas factories hired by Apple are still logging grueling hours and, in some cases, being exposed to dangerous materials without proper training.

“Apple touts itself as a socially responsible leader in the tech industry, but to really be a leader, Apple must put a stop to worker poisoning and ensure sick workers are receiving treatment,” said Elizabeth O’Connell, Green America’s campaign director.

Coming up with a safer manufacturing recipe for the iPhone would cost less than $1 per device, O’Connell estimated. That’s a pittance for a company that earned $37 billion during its last fiscal year.

Neither benzene nor n-hexane is unique to Apple’s manufacturing process. They are also used in the production of electronics products sold by other large technology companies who have also been criticized for their practices. For instance, last year a South Korean court raised doubts about Samsung Electronics’ claims that the benzene levels in its computer chip factories were safe. The court ruled Samsung hadn’t fully examined the health risk in its chip factories after a 29-year-old worker died of leukemia in 2009.

Low levels of benzene are also found in gasoline, cigarettes, paints, glues and detergents.

Apple’s size and success make it an inviting target for groups seeking to draw attention to their causes and perhaps spur changes that are eventually adopted by other companies. Apple boasts a market value of about $480 billion, higher than any other publicly traded company. And the iPhone remains a cultural phenomenon with more than 470 million of the devices sold since the release of the first model nearly seven years ago.

China Labor Watch has been especially harsh in its criticism of Apple, maintaining that the conditions in its manufacturing contractors’ factories are so oppressive that workers are driven to suicide.

Apple CEO Tim Cook, though, has steadfastly maintained that the company’s high standards have led to better treatment of the factory workers and reduced suppliers’ reliance on dangerous substances.

“Since Tim Cook took the helm, Apple’s increased transparency and accountability back down the supply chain has significantly improved, and is quickly becoming a hallmark of his leadership at the company,” Tom Dowdall, a Greenpeace energy campaigner, wrote in a blog post last month.