Sen. Bill Nelson, D-Fla., isn't satisfied with the plans of Verizon Communications Inc. to address privacy concerns with its so-called supercookies, calling for investigations into the company and threatening potential legislation to regulate the Internet tracking technology.

Nelson and other lawmakers on Friday sent letters to the Federal Trade Commission and Federal Communications Commission, urging the agencies to review the legality of Verizon's marketing program that deploys supercookies to follow customers as they surf the web.

Verizon last week announced that it will allow customers to completely opt out of the program. The company in the past permitted users to decline participation in the program, but didn't enable them to reject the identifiers it used for tracking. With the supercookies still in place, advertisers could monitor customers online even if the users didn't agree to the program, security researchers discovered.