This is America.
In America we use grammatical number.
It's "the" ACLU, therefore ACLU is grammatically singular in number and hence takes a verb in the singular: "ACLU Sues," not "ACLU Sue."
If you want to use that King's English rot you should move there and sign up for exorbitant taxation, rotten food, rotten weather, and National Health Care.
Exactly. The operative word is “Union”, which is singular.