Green America, a D.C.-based non-profit group, and The Nation magazine launched a campaign Wednesday intended to persuade consumers to boycott Apple products unless the company makes changes in its production and supply chain operations.

But Apple rejected the call, saying it's been a leader in ridding toxic chemicals from its products and requires its suppliers to match or better U.S. safety regulations.

The campaign is the latest in a string of attempts to get consumers to focus on worker conditions in the myriad of factories that makes Apple products such as iPhones and the components that go into them.

A key message of the campaign is that it would cost just $1 for Apple to substitute out benzene and n-hexane, two of the most toxic chemicals used in its supply chain. The figure was derived from asking industry insiders their "best guess" for the cost involved, said Elizabeth O'Connell, campaign director, Green America.

The campaign is also asking Apple to create a healthcare fund to pay for the care of workers who have fallen sick working on its products, allegedly due to poisoning from those two chemicals, and to generally improve working conditions.

And it's asking consumers to complete a protest letter to Apple CEO Tim Cook and postpone purchases of Apple products until the company makes changes.

Apple products are some of the most popular in consumer electronics and its iPhone leads the smartphone sector, so getting users to click and send a protest letter might be a lot easier than persuading them to put off buying the next iPhone.

"We're hoping that those who are loyal Apple customers will still write to Apple to voice their concerns," said O'Connell. "We know from experience that once you get a certain amount of consumer pressure, the company will listen to that opinion."

China Labor Watch, a New York group that monitors labor conditions in China, joined in support of the campaign to rid the chemicals from the manufacturing process but emphasized it was not calling for a boycott of Apple products.

Apple responded by pointing out that it has led the industry in removing other toxic chemicals from its products, including lead, mercury, brominated flame retardants and PVC.

"When it comes to handling chemicals and toxic substances, we require that our suppliers around the world meet or exceed respected U.S. safety standards such as OSHA, the National Institute for Occupational Safety and Health, and the American Conference of Governmental Industrial Hygienists," the company said in an emailed statement.

"Last year, we conducted nearly 200 factory inspections which focused on hazardous chemicals, to make sure those facilities meet our strict standards. We also provide suppliers with training in hazardous chemical management, industrial hygiene and personal protection equipment as part of the Apple Supplier EHS Academy in Suzhou, China," it said.

Apple and its main iPhone manufacturer, Foxconn, have been criticized for several years over the way workers are treated. The issue jumped to the forefront after a string of suicides at Foxconn factories and pushed Foxconn to pledge a change in the way workers live and are treated. Apple began highlighting the issue in its annual compliance report that also sets targets for its suppliers related to working conditions.

Apple's most recent Supplier Responsibility Report was published last month. It said Apple had conducted 451 audits of its suppliers in 2013.

During the year it dealt with another criticism it has faced in the past, with the verification that none of the tantalum metal used in its products comes from sources that fund armed groups in unstable parts of Africa.

Green America is a Washington, D.C., based non-profit organization. It's currently involved in major campaigns against GMOs (genetically modified organisms) and fossil fuel use in electricity power generation.

Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is [email protected]