NBA owners, who pay the salaries of every member of Team USA as well as dozens of international players participating in the London 2012 Olympics, aren't big fans of their stars playing in extra games over the summer. They're so displeased with subsidizing a popular tournament and taking a huge amount of risk by releasing players for the Olympics that they're in discussions with FIBA to turn the Olympic men's basketball tournament into an under-23 event.
For similar reasons, the men's soccer tournament at the Olympics is an under-23 tournament, though three over-age players are allowed. The NBA owners' concerns seem to have more to do with their international players than their domestic players, because they're less concerned about the medical care that players receive while with Team USA, as well as the judgment of the coaching staff.
There will be a lot of senior international players who won't take kindly to being barred from competing in the Olympics, though it's unlikely that they're going to organize in a fight against the people who sign their paychecks. If the NBA gets their way and the Olympics becomes an under-23 tournament, NBA teams would be more likely to release players during the World Championships cycle, mostly because it could be to their financial benefit. There's talk about re-branding that tournament as the World Cup of basketball, with FIBA and the NBA in partnership that would help both cash in. Currently, NBA owners aren't getting a cut of the money the IOC rakes in from men's Olympic basketball.