Here's the website with the FAQs that state the TWIC is mandated for
all credentialed mariners who use their USCG licenses.
http://www.tsa.gov/what_we_do/layers...s.shtm#general

I wrote a letter to my Senators and congresswoman complaining about
how ridiculous it is for us to be required to pay either $102.25 or
$132.50 to haul folks around for hire on our own boats. And this has
something to do with homeland security or is it just to line the
pockets of some contractor? It states that the USCG and TSA may get
together on this to prevent needless duplication of the merchant
mariner documentation and the TWIC, but in the meantime we have to go
through both processes if your license happens to expire this year.