Fourth Geneva Convention on civilian persons in occupied territories; Russia is a party to this treaty.

https://www.icrc.org/en/doc/assets/files/publications/icrc-002-0173.pdf

Article 51

The Occupying Power may not compel protected persons to serve in its armed or auxiliary forces. No pressure or propaganda which aims at securing voluntary enlistment is permitted.

The Occupying Power may not compel protected persons to work unless they are over eighteen years of age, and then only on work which is necessary either for the needs of the army of occupation, or for the public utility services, or for the feeding, sheltering, clothing, transportation or health of the population of the occupied country. Protected persons may not be compelled to undertake any work which would involve them in the obligation of taking part in military operations. The Occupying Power may not compel protected persons to employ forcible means to ensure the security of the installations where they are performing compulsory labour.

The work shall be carried out only in the occupied territory where the persons whose services have been requisitioned are. Every such person shall, so far as possible, be kept in his usual place of employment. Workers shall be paid a fair wage and the work shall be proportionate to their physical and intellectual capacities. The legislation in force in the occupied country concerning working conditions, and safeguards as regards, in particular, such matters as wages, hours of work, equipment, preliminary training and compensation for occupational accidents and diseases, shall be applicable to the protected persons assigned to the work referred to in this Article.

In no case shall requisition of labour lead to a mobilization of workers in an organization of a military or semi-military character.