The NIH, in addition to its existing public access policy for publications, now requires that those receiving research grant funding from the NIH also take steps to make their research data publicly accessible. Here's a link to the policy:
Effective since 2008.
Effective December 2015.
This plan was developed in response to the White House's Office of Science and Technology Policy’s (OSTP) February 22, 2013 memorandum, “Increasing Access to the Results of Federally Funded Scientific Research."