It's not as black & white as that.
If such a threatening phone call from ATI said you could no longer purchase and integrate ATI products, that would be anti-competetive. If ATI said you would have to pay an extra 20% for all ATI products, that would be monopolistic.
But if ATI said they would no longer co-sponsor some of your advertising or provide validation of their chips in your products, there is nothing inherently wrong with that from an anti-trust standpoint (depending on what standing contracts you have with ATI). It may not be nice, but unfortunately nice and profits don't always go hand in hand.