You can team kill team members a maximum of three times. The third time this happens you will be kicked.
Collateral damage kills count too, because, you could shoot your claymore purposefully to kill a teammate.
There is also the edge case of where you are the host and you won't be kicked. Instead, on action of your third team kill, you will die, and have a 20 second wait, before being added to the respawn cycle. The amount of time you have to wait will increase for every subsequent team kill. I think this is by adding 20 seconds for each subsequent team kill.
You also can't kill someone as soon as the round begins, I think this is around 30 seconds immunity. If you kill them, you will instead die. But this doesn't add to your team kill count and it also doesn't add 20 seconds or give you a 20 second wait.
NOTE: This only occurs for XBox 360 and PS3. PC users have noticed up to 5 team kills before being kicked