SPARC provides a community resource summarizing current federal agency public access policies for both data and articles.  You can select up to three agencies and compare their policies.

On Feb. 22, 2013 the White House Office of Science and Technology Policy (OSTP) released a memo (the Holdren memo) titled, "Increasing Access to the Results of Federally Funded Scientific Research (PDF)." In short, the memo:

"...directed Federal agencies with more than $100M in R&D expenditures to develop plans to make the published results of federally funded research freely available to the public within one year of publication and requiring researchers to better account for and manage the digital data resulting from federally funded scientific research." Michael Stebbins, Assistant Director for Biotechnology at OSTP. 

Links to how each of the agencies chose to implement of Public Access Programs in Federal Agencies can be found in science.gov

It is because of this memorandum that many federal agencies require data management plans. A data management plan should always address plans for making datasets publicly available (or, if they cannot be made publicly available, why). Data management plans should also talk about how the data will be managed to keep it safe and valuable. 

On August 25th, 2022 a new memo was released (the Nelson memo). The new memo affects all federal agencies and directs these to

"Update their public access policies as soon as possible, and no later than December 31st, 2025, to make publications and their supporting data resulting from federally funded research publicly accessible without an embargo on their free and public release"

Important points on this memo are:

• It removes the 12 month embargo for ensuring public access of peer-reviewed scholarly publications.
• There is a requirement to make scientific data underlying peer-reviewed scholarly publications freely available and publicly accessible by default at the time of publication. Data must be protected when needed according to federal laws and OMB policies.
• Federal agencies must also provide guidance to ensure that the repositories used to share scientific data align with the document “Desirable Characteristics of Data Repositories for Federally Funded Research”
• Federal agencies must outline policies to establish researcher responsibilities on how federal data will be managed and shared. This includes how to manage potential limitations to the use and sharing of the data due to legal, privacy, ethical, technical, intellectual property or security reasons. It also includes maximizing appropriate sharing of the data (e.g. establishing limited data access), and specifying an appropriate online digital repository where the data will be deposited.

Because of the Nelson memo all federal agencies will be publishing new policies or updating their old ones in 2024 and 2025.