What You Can Do about unsolicited faxes gives the (US) FCC stance on this. A link at the bottom of the page provides a place to register a complaint.

Federal Communications Commission FCC 03-153 should get you the "new" FCC "Do Not Call" regulation. This is a 562 KB .pdf file of the full regulation, including the associated report and commentary.

The same regulation that prohibits unsolicited voice phone calls to those who register with the US Do Not Call listing also prohibits unsoliceted fax advertising. The exception to allow unsolicited fax to those "with an established business relationship" was deleted sometime in 2003.

The section on FAX is down at Article XIII, page 108.
On page 111:
"189. We now reverse our prior conclusion that an established business relationship provides companies with the necessary express permission to send faxes to their customers. As of the effective date of these rules, the EBR will no longer be sufficient to show that an individual or business has given their express permission to receive unsolicited facsimile advertisements."

WRITTEN PRIOR CONSENT OF A RECIPIENT IS REQUIRED before any advertising fax may be legally sent.

The unsolicited faxes you are receiving are in all likelihood a violation of current FCC regulations and senders are required by US Federal Regulations to cease on your notification to them.
Cost of receipt and processing or $500, whichever is greater, is the established per incident "compensation" that can be demanded if you choose to file suit, and treble damages are permitted if the violation is found to be "willful."

Most States have adopted similar regulations, and you can also check with your state attorney general or trade organizations for local rules. (and compensation possibilities?).

John