A 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:
(1) The use or threat of use of violence or other criminal means to harm the physical person, reputation, or property of any person.
(2) The use of obscene or profane language or language the natural consequence of which is to abuse the hearer or reader.
(3) 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 603(f) or 604(3)1 of this Act.
(4) The advertisement for sale of any debt to coerce payment of the debt.
(5) 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.
(6) Except as provided in section 804, the placement of telephone calls without meaningful disclosure of the caller's identity.
for more go to http://www.ftc.gov/os/statutes/fdcpa/fdcpact.htm#806
I'm not aware of any state where it's illegal to tape, but in some states all parties do have to be notified.
For some strange reason, CAs are more likely to violate the law if they don't know they are being taped.