It depends more on the tracker, and other clients, also, the client you use.
If your client is made by people who like sharing, it will penalize you for low upload rates.
If the other clients in the swarm know you're not uploading much, some of them might not be willing to send anything your way, or throttle what they do send.
If the tracker, and this is particularly true for private trackers, sees that you have a low ratio, overall, then it will throttle what it sends you, trying to keep the playing field fair.
So, in the protocol, nothing specifies that it has to happen, but in common practice, it can, depending on the above.