According to a Library Journal Academic Newswire article, publishers may challenge the provisions of the NIH Public Access Policy mandate if it is made law. The issue arises from the wording of the House bill:
Sec. 217: The Director of the National Institutes of Health shall require that all investigators funded by the NIH submit or have submitted for them to the National Library of Medicine’s PubMed Central an electronic version of their final, peer-reviewed manuscripts upon acceptance for publication to be made publicly available no later than 12 months after the official date of publication: Provided, That the NIH shall implement the public access policy in a manner consistent with copyright law.
Regarding this wording, the Library Journal Academic Newswire article says:
While seemingly innocuous, that language almost certainly will form the basis for a challenge to the policy's implementation. In a letter to lawmakers, the Association of American Publishers (AAP) argued that "a mandate may not be consistent with copyright law," a position emphasized by Brian Crawford, chair of the AAP's Professional and Scholarly Publishing Division Executive Committee. "The copyright proviso in the Labor/HHS Appropriations language does not in itself provide sufficient assurance of copyright protection," Crawford told the LJ Academic Newswire. "The mandatory deposit of copyrighted articles in an online government site for worldwide distribution is in fundamental, inherent, and unavoidable conflict with the rights of copyright holders in those works."