In order to access Mass Effect 2's "Cerberus Network," which provides in-game access to a store to purchase downloadable content and will be the only way to receive certain free downloadable content that BioWare issues in the coming months, you must buy a new copy. Anyone who purchases a used copy of Mass Effect 2 will need to spend $15 to access the Cerberus Network.
This practice against used games started in December with EA's The Saboteur. In Pandemic Studios' last release as an external studio, the ability to see females in the game's brothels without their tops was by purchasing a new copy of the game. Used copies required gamers to fork over $5.
$15 is a bit different than $5. The difference in price hopefully reflects how serious BioWare and EA are taking the measure, and how they're both planning to reward gamers appropriately for their decision.