This is story related and unlocks naturally.
*** Spoiler - click to reveal *** After you celebrate New Years, you will be ordered by the General to confiscate excess green stuff. A soldier will tell you about a civilian who is "hoarding" green stuff and must be made to share with everyone. Basic filthy Communist bullshit. The civilian is Petrovich, the guy who drove you back home from the sewers. He tells you he's been saving the green stuff from his own wages and is using it for his sick granddaughter, who needs more medication than normal. You will be given a choice: order your men to confiscate every single vial in his room (right), or just take what is necessary and be on your way (left). After you make the choice, the cutscene will end a couple minutes later, and the achievement will unlock.
FYI: irrespective of what you choose to do, it has no real impact on the outcome of the story. The only thing that changes is the dialogue between the two of you later on.