Sen. Maggie Hassan (D-N.H.) sent an open letter to the Entertainment Software Rating Board (ESRB) today urging the industry’s self-regulatory body to “review the completeness of the board’s ratings process and policies as they relate to loot boxes and to take into account the potential harm these types of micro-transactions may have on children.”

Loot boxes—which offer randomized in-game rewards, often in exchange for real money— concern Hassan for the “psychological principles and enticing mechanics that closely mirror those often found in casinos and games of chance,” as the letter reads. While acknowledging “robust debate over whether loot boxes should be considered gambling,” Hassan argues that “they are both expensive habits and use similar psychological principles” and thus deserve extra scrutiny. “The potential harm is real.”

Hassan urged the ESRB in the letter to examine whether loot boxes were being marketed “in an ethical and transparent way that adequately protects the developing minds of young children from predatory practices.” She also asked the board to “collect and publish data” on how developers and players use loot boxes.