The most common and most likely answer to this crossword clue is the 6 letter word OPPUGN
I've seen this crossword clue in The Times
O
P
P
U
G
N
More clues leading to the result OPPUGN
- Setting up position to hold back attack
- Rang up policy section about dispute
- Ridiculous popgun challenge
- Some bang up politicians over dispute
- Workdog, say faces new dispute
- Call into question popgun that’s shot
- Call into question work finally undertaken by dog
- Challenge old dog within confines of prison
Buddy explains!

The straight part
We know that "dispute" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dispute = oppugn.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.
What does OPPUGN mean?
OPPUGN verb- To contradict or controvert; to oppose; to challenge or question the truth or validity of a given statement.