The deposit usually isn't charged to your credit card, rather it's just a hold. So it goes into your available credit, but doesn't add to your balance, and thus the initial "hold" doesn't show up on your credit card. So if it was in fact $3,000 then the card would decline if you didn't have that much available.

I agree with jackal, I think it's poorly worded or a mistake. Most North American locations hold a maximum of 20% over the rental total to cover additional fees that might be incurred. So keeping the math simple, if your total was $300, the hold would be for $360. You'd have $360 less available credit than when you walked up to the counter, but provided you returned the car on time, refueled, and undamaged, you'd only see a $300 charge on your statement. The remaining $60 would be freed up within a couple of days to be used again.