...I just found it. Have never used it.
http://www.tpc.int/faxbyemail.htmlBe sure to check coverage area:
http://www.tpc.int/verify.htmlFrom the Electronic Frontier Foundation:
Presently, neither the House nor the Senate provide a fax list of legislators, to our knowledge. Many legislators' fax numbers are available from the Project Vote-Smart Elected Official Biographical Information Database at
http://www.vote-smart.org/ce/. If that fails, you can look up your Representative's Web page in a list by name at
http://www.house.gov/MemberWWW.html, or on an interactive form by your ZIP+4 code at
http://www.house.gov/writerep/; and your Senator's Web page by state at
http://www.senate.gov/senators/senator_by_state.cfm or by name at
http://www.senate.gov/senators/.If your legislator's fax number is not available via these means, you will have to call his/her office and ask for it. Say that you are a constitutent trying to contact the legislator via fax with your opinions on an issue before Congress. They may refuse to divulge the number - some of the more backward Congressional offices seem to believe that fax machines are only for inter-office use, and not a normal means for the public to contact legislators. If this happens to you, POLITELY express your displeasure at this position, deliver your opinion on the issue via the phone, and then send a postal letter with the full comments you had hoped to fax, closing with a p.s. that you would rather have faxed it, and are disappointed that your legislator's office does not provide a fax number for constitutents to send comments to.
We are always on the lookout for a comprehensive and regularly maintained Congressional fax number list. If you happen to encounter one, please let us know at ren@eff.org.
http://www.eff.org/congress/#phonefax