Yes, PREEMPTION is a Scrabble word!

Letter values in Scrabble US: P 3, R 1, E 1, E 1, M 3, P 3, T 1, I 1, O 1, N 1.

Is it a valid word?

PREEMPTION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the judicial principle asserting the supremacy of federal over state legislation on the same subject
the right of a government to seize or appropriate something (as property)
the right to purchase something in advance of others
a prior appropriation of something

Also: pre-emption.