said on Thursday that it would allow shoppers to trade-in used videogames for store credit, a move that may challenge a core driver of profitability for game retailer GameStop.

Shares of GameStop, the biggest U.S. videogame retailer, had risen 35 percent in the past 3 months as sales of video game consoles by Nintendo, Sony Corp and Microsoft remained robust, driving consumers into GameStop stores games to buy software for their systems.

However, its profit margins have benefited from an active trade-in system, where shoppers return used games for a fraction of the purchase price or credit toward future sales. The returned games are sold at a higher profit margin than new games.

Shares of GameStop fell $4.04 to $23.26, while Amazon shares were off 31 cents at $64.50.

(Reporting by Franklin Paul; Editing by Tim Dobbyn)