It threatens "follow up notices" with no doubt information about if the voter voted in the caucus.
It intends to intimidate a person into voting by threatening to disclosure to the neighbors the person's voting record.
What does Ted Cruz expect the person receiving this notice to do to their neighbors for not voting as he demands?
What might happen to the voter if the neighbors are informed the voter has not voted as Ted Cruz expects?
These are direct threats and intimidations in violation of federal election, civil rights, and postal laws.
The following PDF document link outlines the federal election laws and the government's position on such matters for the purposes of prosecution.
Federal Prosecution of Election Offenses Seventh Edition, May 2007
The following sections are from the above document. I've condensed and paraphrased the document to the important words.
42 U.S. Code § 1973gg-10 - Criminal penalties (violation of election law)
A person in any election for Federal office knowingly and willfully intimidates, threatens, or coerces, or attempts to intimidate, threaten, or coerce, any person for registering to vote, or voting, or attempting to register or vote; urging or aiding any person to register to vote, to vote, or to attempt to register or vote; shall be fined or imprisoned not more than 5 years, or both.
18 U.S. Code § 594 - Intimidation of voters
Whoever intimidates, threatens, coerces, or attempts to intimidate, threaten, or coerce, any other person for the purpose of interfering with the right of such other person to vote or to vote as he may choose, or of causing such other person to vote for, or not to vote for, any candidate for the office of President or Vice President shall be fined under this title or imprisoned not more than one year, or both.