"damela" vs. "dame"

I am confused about whether "la" is required in the following sentence:

Damela una taza de té, por favor.

Would it also be correct to drop the "la" and say:

Dame una taza de té, por favor.

I was wondering if there was a rule that I can follow. I'm always finding myself confused over whether or not the direct object pronoun is necessary.

Thanks!