According to the US Code Title 18 Section 595:
Whoever, being a person employed in any administrative position by the United States, or by any department or agency thereof...uses his official authority for the purpose of interfering with, or affecting, the nomination or the election of any candidate for the office of President, Vice President, Presidential elector, Member of the Senate, Member of the House of Representatives, Delegate from the District of Columbia, or Resident Commissioner, shall be fined under this title or imprisoned not more than one year, or both.
I'm not a legal expert, but as far as I can tell, Postmaster DeJoy is a person employed by the United States government, is using his official authority as leader of the USPS, for the purpose of affecting the 2020 presidential elections by reducing the capabilities of the USPS to process mail-in ballots. Am I missing something here, or are his actions indeed a violation of federal law?