FTC.gov's web site states: "an e-mail recipient cannot be required to pay a fee, provide information other than his or her e-mail address and opt-out preferences, or take any steps other than sending a reply e-mail message or visiting a single Internet Web page to opt out of receiving future e-mail from a sender"
http://business.ftc.gov/documents/bus61-can-spam-act-complia...
Current FTC rules say that your unsubscribe link must either immediately unsubscribe the user or lead to a page that (at most) asks for only your email address and does not try to confuse or dissuade you.
If you're fluent in legalese, it's in the set of rules known as "CAN-SPAM 2008" http://www.ftc.gov/os/2008/05/R411008frn.pdf
So I guess your best bet is to file a complaint with the FTC, which does occasionally sanction companies, or with your state attorney general, who also has the power to force action.
(You could argue that such mail isn't "real" spam; nonetheless, "mark as spam" is realistic.)