Landis was a teammate of Armstrong on the Postal Service-sponsored team from 2002 to 2004, and his lawsuit was filed under the False Claims Act, the Justice Department said. That act is commonly called the whistle-blower law.

The law permits the federal government to investigate allegations and intervene, the Justice Department said.

The act was originally passed in 1863 when government officials were concerned that suppliers to the Union Army during the Civil War could be defrauding them.

In 1986, Congress modified the law to make it easier for whistle-blowers to bring cases and give them a larger share of any penalties collected. Whistle-blowers can now take home between 15% and 30% of the sums collected in their cases.

For years, Armstrong had denied drug use and blood doping, but he publicly admitted such use in January, three months after international cycling's governing body stripped him of his seven Tour de France titles.

That stripping came after a damning report by the U.S. Anti-Doping Agency accused Armstrong and his team of the "most sophisticated, professionalized and successful doping program" in cycling history.

That agency praised the Justice Department's announcement.

"The U.S. Postal Service Cycling Team was run as a fraudulent enterprise and individuals both inside and outside of sport aided and abetted this scheme and profited greatly," CEO Travis T. Tygart said in a statement.