A new report released this week has found that of the big electronic firms like Apple, Microsoft, Sony and Samsung, only Nokia can prove that it pays its factory workers a living wage. The report, compiled by Not For Sale in the U.S. and Baptist World Aid in Australia, looked at the supplier working conditions at 39 of the world's biggest tech companies and found that, with the exception of Nokia, all were unable to prove that their factory workers are paid a livable wage. Only half of the companies could identify all their suppliers at the final stage of production and less than one fifth of the companies could accurately confirm the source of their raw materials.

"More than ever before, the world is asking questions about the people making our electronics and the conditions under which they work," the report says. "Interest has been spurred on by the ascendency of global brands like Apple, Microsoft and Samsung, combined with growing public concern about exploitation and child labor in Chinese electronics factories, as well as fears about the use of conflict minerals sourced from the Democratic Republic of Congo (DRC)." The report aims to expose the labor working conditions at these companies, and follows similar reports by this group on the apparel industry and coffee production.

The report titled "The Truth behind the Barcode: Electronic Industry Trends" shows that there is much room for improvement. Even though Nokia is alone in being the only big tech firm in the study that could prove it paid its factory workers a living wage, it still only scored a B+ overall. The companies were graded across four categories of their Corporate Social Responsibility (CSR) practices: policies; traceability and transparency; monitoring and training, and workers' rights.

Apple, LG Electronics, Microsoft and Samsung among others also scored a B overall, albeit with lower scores than Nokia. The report is quick to point out that Apple's ranking may be surprising given the media attention the iPhone maker has received for poor working conditions and child labor at its suppliers Foxconn and Pegatron. But Apple's ranking near the top is due to the fact that many of these companies received a B not because their supply chains are free of abuse, but because they are doing more to address these issues.

Apple, for its part, released its eighth annual supply chain report this year that found 23 underage workers at its suppliers' facilities. In 2013, Apple's audit uncovered 74 underage workers at a single supplier. The latest report also found that Apple's suppliers achieved an average of 95 percent compliance with its standard maximum 60 hour work week.

Blackberry, Hitachi and IBM were among the companies that scored a C grade overall. Amazon Kindle, HTC, Huawei and Nintendo scored a D grade overall. While Hisense and Palsonic were the only two companies to receive an F.

It's important to note that almost every company with an ethical sourcing policy requires supply chain workers to be paid either a legal minimum wage or an industry standard wage, which are often comparable. However, the local legal minimum wage in many developing countries is not enough to meet basic living needs. Therefore, Nokia is alone in being the only major tech company that can prove its factory workers are paid above the local legal minimum.

According to the report, Microsoft and Samsung also claim to pay above minimum wages, but did not provide sufficient evidence at the time of publication. Nokia was also alone in being the only company that was able to identify factories where collective bargaining, which goes a long way to bringing wage increases, existed. The report found that only a third of the major tech companies it studied allowed its supply chain workers to engage in collective bargaining.

While the grades for the companies might seem arbitrary, given that they reflect what the companies are doing about its labor working conditions rather than the current conditions, addressing workers abuse is the first step in fixing the problem. "If companies don't know or don't care who is producing their products, it's much harder to know whether workers are being exploited or even enslaved," Baptist World Aid advocacy manager Gershon Nimbalker told Sky News. Read the full report here.