A man walks in front of a company logo outside an Apple store in downtown Shanghai January 24, 2013. (REUTERS/Aly Song )

A new report from China Labor Watch and the environmental group Green America claims Apple hasn't adequately responded to complaints from the groups to improve worker safety at one of its assembly plants in China. The groups published their report based on information gathered from visits to the plant, owned by a supplier called Catcher Technology. The plant, located in Suqian, China, produces and polishes metal for the cases of Apple products. The labor advocacy groups said that the Catcher plant forces its employees to work excessive hours in unsafe conditions.

The groups have had some success grabbing Apple's attention in the past. After China Labor Watch and Green America petitioned the tech giant to stop using dangerous chemicals in its plans, Apple said it would stop the use of two chemicals in its final assembly plants. But on Thursday, the groups said that they informed Apple of these dangerous conditions at the Catcher plant in 2013, yet still found the problems when an investigator returned to the plant in 2014.

According to the report, the Catcher plant is particularly dangerous, due to flammable dust produced by the metal shavings at the plant, which caused two Apple factory explosions in 2011. The report, based on observations and interviews from an undercover investigator who spent nearly two weeks as a Catcher employee and spoke with 100 workers, also found that workers have little or no access to unions or labor protection groups. The report also states that several student workers -- between 16 and 18 years old -- were working at least 10 hour days in violation of local labor laws and Apple's own 60-hour weekly work limit for its factories.

In a statement, China Labor Watch coordinator Kevin Slaten said, "This is exploitation by the factory and Apple for the sake of profit maximization.”

The majority of tech firms that make products -- Microsoft, Samsung, Amazon, Sony and Hewlett-Packard, to name a few -- have faced sharp criticism about the treatment of workers in their plants.

But perhaps no company has gotten as much criticism as Apple, which labor advocates and consumers have called upon to lead the industry in improving conditions in its vast network of Chinese factories and assembly plants. Cracking down on underage workers, improving safety conditions and facilitating better worker-factory relationships have been three of Apple's stated goals as it audits its supplier chain. Last year, the company said, Apple conducted "451 audits deep into our supply chain so we could uncover problems and work with our suppliers to fix them."

The company has scrutinized Catcher, the factory that is the subject of the new report, before, Apple said in a statement Thursday. The firm said it has already had to remedy problems with the factory's fire-safety protocols -- such as the presence of broken fire extinguishers, blocked corridors and unlabeled fire exists. But, Apple said, Catcher has consistently exceeded safety standards in audits of its operations and has averaged 95 percent compliance with Apple's company work limit.

In response to the report, Apple said it will send more inspectors to the plant to assess the claims. "Our most recent annual audit, in May, found some concrete areas for improvement in Catcher’s operations, and we worked with Catcher to develop a corrective action plan," the statement said. "We had scheduled a follow-up visit next month to review their progress but have dispatched a team there immediately to investigate this report."