The protest is due to poor training conditions for swimmers and coaches including decrepit facilities.
Hosszu, who won three gold medals and a silver in Rio and holds multiple world records, blamed the head of the Hungarian Swimming Federation (MUSZ) Tamas Gyarfas for poor training conditions for swimmers and coaches including decrepit facilities in an open letter posted on her Facebook page Tuesday.
She also accused Gyarfas of administrating the sport in an undemocratic manner.
"If Hungarian swimming is in fact important for Tamas Gyarfas...he should resign from his post," said Hosszu.
Her stance has been publically backed by other top swimmers including Daniel Gyurta, gold medal-winner at the 2012 Olympic Games, and Boglarka Kapas, who won a bronze in Rio.
"Unfortunately things really aren't in order in Hungarian swimming, and it's time to talk openly about it," Kapas said in a statement to the Nemzeti Sport daily newspaper Wednesday.
On Thursday Olympic swimmers David and Evelyn Verraszto, Peter Bernek, and Dominik Kozma also joined the protest.
Gyarfas has refused to resign so far while federation officials have called for dialogue and asked the swimmers to come up with a list of specific demands.
The Hungarian capital Budapest is scheduled to host the World Swimming Championships in 2017.