15 U.S. Code § 1692d - Harassment or abuse
Harassment or abuseA debt collector may not engage in any conduct the natural consequence of which is to harass, oppress, or abuse any person in connection with the collection of a debt. Without limiting the general application of the foregoing, the following conduct is a violation of this section:
The use or threat of use of violence or other criminal means to harm the physical person, reputation, or property of any person.
The use of obscene or profane language or language the natural consequence of which is to abuse the hearer or reader.
The publication of a list of consumers who allegedly refuse to pay debts, except to a consumer reporting agency or to persons meeting the requirements of section 1681a(f) or 1681b(3)  of this title.
Causing a telephone to ring or engaging any person in telephone conversation repeatedly or continuously with intent to annoy, abuse, or harass any person at the called number.
Except as provided in section 1692b of this title, the placement of telephone calls without meaningful disclosure of the caller’s identity.
 See References in Text note below.