Lance Armstrong is suing a former personal assistant who claims the six-time defending Tour de France champion owes him $US500,000 ($A659,500).

In a lawsuit filed on Monday, Armstrong and his personal service company, Luke David LLC, are seeking to declare an alleged employment contract with Mike Anderson invalid.

Anderson claims that Armstrong sent him an e-mail in 2002 setting proposed terms of employment, according to papers filed in the lawsuit.

Anderson, who helped Armstrong with training and landscaping, alleges the e-mail served as a contract. But papers in the lawsuit stated he could be terminated at will.

After being fired in November, Anderson demanded Armstrong and his company pay $500,000 to he and his wife, the lawsuit states.

Anderson also demanded a signed Tour de France jersey and future endorsements from the cycling champion.

Armstrong's agent, Bill Stapleton, did not immediately return a telephone message from The Associated Press. Anderson could not be reached for comment.

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