Marathon officials are threatening to demand repayment for millions in prize money awarded to Liliya Shobukhova, a Russian runner who has received a two-year ban for doping.
Russian sports officials annulled Shobukhova's results dating back to 2009, which would include three victories in the Chicago Marathon and one in London.
Shobukhova can appeal the ruling.
The World Marathon Majors series -- which includes races in Chicago, London, Boston, New York, Tokyo and Berlin -- has a policy stating "any athlete found guilty of a doping offense will be required to repay any prize or appearance money."
"Cheats need to understand that they are not welcome in our sport and that they will be caught,” Nick Bitel, the organization's general counsel, said in a statement Tuesday.