Should TPAs be using circular 230 disclosure on letterhead/e-mail/fax correspondence?

Circular 230 does not directly apply to TPAs, only to professionals who give tax advice. Some TPA firms may in fact be subject to the 230 rules, but many will not. Each firm should confer with its legal counsel and make a determination of whether they may be providing tax advice, and, if so, what sort of disclaimer should be used for each type of communication.
For example, even if the firm considers that an actuary's letter advising the client as to the maximum tax-deductible contribution for a year to be tax advice, a letter from the same actuary requesting year-end census information would not. Similarly, a TPA firm may calculate the ADP and ACP amounts and appropriate refunds for a year, and advising a client on those issues may be construed as tax advice, but other services provided will not be.