I read this quote in a Guardian article a while back and have been questions the legality ever since.
You can look at Nixon’s returns at the Presidential Tax History Project. You can look at Trump’s 1995 returns at the New York Times. If you can somehow see Trump’s later returns, feel free to send copies along to our offices at 222 Broadway, New York.
It is the last part of this that is of interest
If you can somehow see Trump’s later returns, feel free to send copies along to our offices
According to law.cornell.edu
(c) Disclosure of returns and return information to designee of taxpayer ---------------------------- The Secretary may, subject to such requirements and conditions as he may prescribe by regulations, disclose the return of any taxpayer, or return information with respect to such taxpayer, to such person or persons as the taxpayer may designate in a request for or consent to such disclosure, or to any other person at the taxpayer’s request to the extent necessary to comply with a request for information or assistance made by the taxpayer to such other person. However, return information shall not be disclosed to such person or persons if the Secretary determines that such disclosure would seriously impair Federal tax administration.
Now, according to California Law, actively encouraging/calling for the committing of a crime can be considered a crime itself. To me, asking someone to divulge confidential information is calling for the committal of a crime.
Issue of my post: I only know the California Law because that's what google gave me first.