Russian swimmers Vladimir Morozov and Nikita Lobintsev on Saturday launched the first challenge against International Olympic Committee sanctions excluding them from the Rio Olympics.
The Court of Arbitration for Sport (CAS) will hold swiftly convened hearings in Rio to decide on the appeals by the two, both medal winners for Russia at past Olympics.
Morozov, 24, and Lobintsev, 27, have called on CAS to declare "invalid and unenforceable" an IOC order for federations to exclude athletes implicated in an investigation on doping in Russia.
Morozov and Lobintsev were among seven Russians banned by the International Swimming Federation (FINA) last week after the order.
A report by Canadian lawyer Richard McLaren for the World Anti-Doping Agency (WADA) said there had been state-run doping, aided by the Russian secret service, at the 2014 Sochi Winter Olympics.
Rejecting calls for a blanket ban on Russia, the IOC decided on July 24 that individual sports federations should investigate athletes implicated in the report and decide who should be excluded.
So far at least 117 individuals from the 387 that the Russian Olympic Committee wanted to enter have been excluded.
Morozov, a member of the 4x100m freestyle relay team that took bronze at the 2012 London Games, and Lobintsev, winner of a silver in the 4x200m freestyle team in Beijing in 2008, have taken their action against the IOC and FINA.
"Both swimmers request CAS to declare the decision of the IOC executive board of July 24 2016 invalid and unenforceable," said a CAS statement.
"The swimmers also request that the decision of the FINA bureau of July 25 2016, declaring both of them ineligible for the Olympic Games in Rio, be set aside."
Morozov and Lobintsev also demand that the IOC "validates the entries submitted by the Russian Olympic Committee for them to compete in the Olympic Games in Rio."
CAS did not say when a decision would be announced.