They do, (thanks, Arrkk) and that’s a better answer.

But the schoolmarm in me brings me back to tell you that, because of the “y-” in the way “union” is pronounced, standard usage is “a union” even though it starts with a vowel. The reason we use “an” is to avoid an awkward slide from the a to the vowel, but in words that start with the “you-” sound it’s not necessary.

A ugly bastard An ugly bastard

A onion An onion

An unicorn A unicorn

That’s me done, and a gold star to you on catching my original error!