More Amazon customers push cloud giant to increase renewable energy use by Barb Darrow @FortuneMagazine June 4, 2015, 9:02 AM EDT E-mail Tweet Facebook Linkedin Share icons Thousands of companies use Amazon Web Services to power their businesses. Last year the company claimed more than 1 million “active customers” of its cloud infrastructure in all. Now a growing number of those customers are pushing the cloud giant to be more open about what’s powering its data centers and are pushing it to use more green, renewable energy sources. According to the Wall Street Journal, 19 AWS customers including Hootsuite, Tumblr YHOO , and Upworthy, wrote to Amazon AMZN Senior Vice President Andy Jassy to open up about the company’s carbon footprint and what steps it’s taking to reach energy efficiency goals. The letter, also signed by Change.org, the Huffington Post, Thoughtworks and others, is here. Last week, Netflix NFLX , one of Amazon’s biggest customers, blogged that it wants its data center providers to commit to 100% clean energy, at the very least by paying for renewable energy credits. The video streaming service also allocates its workloads to take advantage of Amazon’s greenest facilities. Per the blog, “Netflix relies more heavily on AWS regions that are powered primarily by renewable energy (including the carbon-neutral Oregon region), our energy mix is approximately 50% from renewable sources today.” In November, Amazon stated a “long-term commitment to achieve 100% renewable energy usage for our global infrastructure footprint.” But details were sparse. In a recent update, the company said that as of April, about 25% of power used by its global infrastructure is from renewable sources. The goal is to raise that percentage to at least 40% by the end of 2016. Fortune reached out to Amazon for comment and will update as needed. Watchdog group Greenpeace has been hounding Amazon to get more transparent about its energy usage and plans to go greener. It has given Google GOOG , Apple AAPL , and Facebook FB better grades, both on their transparency and their use of renewable energy. The day after this story posted, an Amazon spokesman got back with a link to this post by evangelist Jeff Barr which claimed that Amazon cloud customers use 77% fewer servers and 84% less power than busineses that run their own data centers. Subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology. NOTE: This story was updated on June 6 2015 at 11:10 a.m. EDT.