A tamper resistant attachment apparatus for attaching a backrest to a chair frame. A flap is foldably coupled to an edge of a chair backrest. The flap is foldable over onto the backrest into a folded position. The flap has a channel that fits around a frame of a chair when the flap is in the folded position. At least one aperture that extends through the flap can receive a corresponding pin that is coupled to the backrest when the flap is in the folded position. The at least one pin is deformable to secure the flap and backrest around the chair frame when the flap is in the folded position.