The most common and most likely answer to this crossword clue is the 10 letter word NON-VOTING
I've seen this crossword clue in The Guardian
N
O
N
-
V
O
T
I
N
G
More clues leading to the result NON-VOTING
Buddy explains!

The straight part
We know that "Unable to say yea or nay" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unable to say yea or nay = non-voting.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.