Up to 31 athletes from six sports could be banned from Rio 2016 after the International Olympic Committee (IOC) retested doping samples from the 2008 Games in Beijing.
The tests focused on those who could potentially appear in the Brazilian city and used the latest scientific methods.
A special meeting of the IOC Executive Board (EB) was held today to discuss the issue.
"This is a powerful strike against the cheats we do not allow to win,” said IOC President Thomas Bach.
In total, 454 samples were selected from the Beijing Games, with the re-tests following work with International Federations and the World Anti-Doping Agency (WADA).
The EB agreed unanimously today to initiate proceedings against the 31 athletes - who come from 12 countries - immediately.
The IOC has also announced that the results of 250 retests from London 2012 will also be announced shortly.
"The aim is to stop any drugs cheats coming to the Olympic Games in Rio de Janeiro," a statement said, with no indication yet of who the athletes implicated are, or if any medals will be reallocated.
Today's announcement could be seen as an attempt by the IOC to garner some good press following a spate of doping scandals across sport.
This month the IOC has been rocked by damning allegations about Russian interference in the doping laboratory at the Sochi 2014 Winter Olympics.
Grigory Rodchenkov, the former head of Russia's discredited doping facility in Moscow, sensationally detailed an alleged state-run cover up of drugs offences in The New York Times.
The IOC has now promised "swift and decisive action" following this controversy, with WADA asked to initiate a "fully fledged investigation" into the Sochi allegations.
The Lausanne Anti-Doping Laboratory, where the Sochi samples are stored for ten years, will be ordered to cooperate with WADA, and the Russian Olympic Committee have been instructed to provide their full assistance.
Richard Budgett, the IOC's Medical and Scientific Director, has been put at WADA's disposal.
"Based on the result of this investigation the IOC will take swift action," the IOC claimed.
Bach said that dopers have "no place to hide".
"The re-tests from Beijing and London and the measures we are taking following the worrying allegations against the laboratory in Sochi are another major step to protect the clean athletes irrespective of any sport or any nation," said the German.
"We keep samples for ten years so that the cheats know that they can never rest.
“By stopping so many doped athletes from participating in Rio we are showing once more our determination to protect the integrity of the Olympic competitions, including the Rio anti-doping laboratory, so that the Olympic magic can unfold in Rio de Janeiro.”