The lawsuit by Landis, who was stripped of the 2006 Tour de France title after testing positive, alleges that Armstrong defrauded the U.S. government by repeatedly denying he used performance-enhancing drugs. The deadline to join the False Claims Act lawsuit, which could require Armstrong to return substantial sponsorship fees and pay a hefty penalty, is Thursday.
Landis is hardly the only one seeking money back from Armstrong.
During his long reign as cycling champion, Armstrong scolded some critics in public, didn't hesitate to punish outspoken riders during the race, and waged legal battles against still others in court.
The London-based Sunday Times has already filed a lawsuit to recover about $500,000 it paid Armstrong to settle a libel case, and Dallas-based SCA Promotions, which tried to deny him a promised bonus for a Tour de France win, has threatened to bring another lawsuit seeking to recover more than $7.5 million awarded by an arbitration panel.
In Australia, the government of the state of South Australia said it will seek the repayment of several million dollars in appearance fees paid to Armstrong for competing in the Tour Down Under in 2009, 2010 and 2011.
"We'd be more than happy for Mr. Armstrong to make any repayment of monies to us," South Australia Premier Jay Weatherill said.
Litke reported from Chicago, Vertuno from Austin, Texas. Pete Yost in Washington and John L. Mone in Dearborn, Mich., also contributed to this report.