According to witnesses, police divide those at the gym into citizens and non-citizens. Russians are taken to enlistment offices, where their military records are checked.
Non-citizens are accused of immigration violations and given a choice: deportation, or enlistment in the army, according to Current Time, an independent Russian news platform.
On the same topic: https://meduza.io/en/feature/2025/04/08/russian-police-are-raiding-gyms-sweeping-up-men-for-conscription-and-deportation