Twenty-eight Australian swimmers have pulled out of the ISL event in Budapest in Hungary, due to run from from October 16, because of concerns over COVID-19.

According to Swimming World Magazine, Cate and Bronte Campbell and Emma McKeon of London Roar, and Cali Condor swimmers Ariarne Titmus and Mitch Larkin were not prepared to risk travelling to Europe while the continent battles to stop the spread of coronavirus.

Their decision to withdraw is a blow to the ISL, which has put in a number of measures to combat COVID-19, including holding the event behind closed doors.

Swimmers will also be expected to have four COVID-19 tests - two before making the trip - before they will be allowed to train, assuming the results come back negative.

The ISL chose not to single out any National Federation but its statement appears to point the finger at Swimming Australia.

"The current health crisis should not be used to entrench existing vested interests," the ISL statement read.

"It is unacceptable that some national swimming federation’s leaders, knowingly and cynically use the pandemic to intimidate athletes who wish to participate in other competitions.

"Athletes must be protected not only in their physical integrity but also in their economic and social integrity.

"They need to compete or risk imperilling their livelihoods.

"ISL stands for the right of all athletes to freely live their swimming life, believes it is time to put power back into their hands, to champion their right to make a living they deserve, and to have a greater say in the way their sport is run.

"The recent bullying and pressure on some of the athletes who are already in a precarious position is a political manoeuvre and contrary to the very spirit of sport."

It is understood Emily Seebohm, who swims for reigning champions Energy Standard, and DC Tridents duo Leiston Pickett and Tristan Hollard are among a small Australian contingent who are still considering attending.

Budapest has been selected to hold 10 qualifying races, taking place between October 16 and November 16, before staging the semi-finals from November 19 to 22.

Speaking to Swimming World Magazine, Rob Woodhouse, general manager of London Roar, said the team was "pretty devastated" by the withdrawals but backed the swimmers’ decisions.

"It’s the uncertainties of the travel itself, the health and safety issues and getting back into the country because it is so hard to get flights and potentially having to stay away with quarantines and the final may not be until December, there are so many unknowns," Woodhouse said.

"From a London Roar perspective we totally support the swimmers decisions and we are as devastated as they are; all the athletes have said how much they enjoyed the ISL last year and wanted it to be back with the Roar and part of it again.

"Some saying it is the best thing they have ever done in the sport.

"It was each individual’s choice; they had to make up their own minds because there is a lot at stake here."