President Obama has been pushing for tougher gender pay legislation and the state of California recently passed legislation mandating equal pay for equal work. Activist investor Arjuna Capital asked nine tech companies, including Apple, Google and Amazon to reveal pay gaps and develop a plan to improve them. Amazon was the only company to resist, claiming Arjuna's proposal was too "vague." It asked the SEC if it could exclude the proposed ballot from its shareholder filing, but the regulator sided with Arjuna. As a result, Amazon voluntarily released the results after surveying employees.

"There will naturally be slight fluctuations from year to year, but at Amazon we are committed to keeping compensation fair and equitable," the retail giant told the WSJ . In comparison, Apple also says it pays equally (other than stock options), while its workforce is just 31 percent female. However, women hold more management positions at Apple (28 percent), even though the executive suite is overwhelmingly male. In terms of overall diversity, Amazon is on nearly equal footing with Facebook and Google, and is considerably better than Microsoft. Overall, tech diversity is abysmal in the US compared to other sectors. (See our diversity report for 2015 tech company stats.)