If the work is normally unpaid (like contributing to open-source projects), then it's fine. Quoting from http://www.cilawgroup.com/news/2013/10/15/unpaid-volun

If the work is normally unpaid (like contributing to open-source projects), then it's fine. Quoting from http://www.cilawgroup.com/news/2013/10/15/unpaid-volunteer-work-on-h-1b-h-4-f-1-or-similar-visas/ http://www.cilawgroup.com/news/2013/10/15/unpaid-volunteer-w... : "As a general rule of thumb, one should look at whether Americans would perform the same job without pay and under similar circumstances and if the answer is “yes,” then a foreign national in an employment-restricted status can volunteer and work without pay."