According to Murray Chass on Sunday (hat tip to Baseball America):
Bud Selig has repeatedly cautioned clubs about the economy, and at the owners’ meeting last Thursday he told them he was doing something about it and sternly advised them to listen. The commissioner told the owners that his office planned to roll back the recommended signing bonuses for the June 9 amateur draft by 10 percent.
Baseball America's Jim Callis confirmed Selig's plan. The slots are confidential, but BA has estimates for last year's recommendations if you're a subscriber. So what's the penalty for going over slot? According to Chass:
Clubs enrage Selig when they exceed their slotted numbers, and he lets them know his feelings.
Scary! Callis' take:
MLB can’t force teams to accept its recommendations, but it has exerted pressure on owners to toe the line and fined clubs that didn’t follow a set procedure before paying an above-slot bonus.