The Washington Post reports that US Federal Law punishes the unauthorized publication of tax information. In addition, New York law deems unlawful the disclosure of “the amount of income or any particulars set forth (…) in any report”, and the legislation of New Jersey punishes with up to 18 months of prison time “any person … divulging, disclosing or using [tax] information”.
If sued, the immediate best defence to resort to for the Times would be one based on First Amendment. As the Post notes, claiming the superior “public interest” of the news would not necessarily be enough. In the words of Jonathan Zittrain from Harvard Law School “the courts could say, if the public thinks the tax returns are so important, let it demand that the candidate authorize the IRS to release them on pain of losing votes.”
Concurring Opinion posed to 11 experts the question of how likely would a First Amendment defence hold in a prosecution against the New York Times. The general conclusion is that the publication of the documents would probably remain unpunished, unless the paper participated in their unlawful acquisition.