According to Romulusz Ruszin-Szendi, participation in the military training program was not completely voluntary, the Prime Minister's Office rejects this

The former Chief of Staff stated that he has letters that prove that participation in the program was not entirely voluntary. The Prime Minister's Office wrote to Telex that they categorically reject this.

The former chief of staff has letters in his possession saying it was “very warmly recommended” for officers to attend basic defense training.

But then what is this volunteerism like?

It was "highly recommended."