The most common and most likely answer to this crossword clue is the 6 letter word QUOTAS
I've seen this crossword clue in Financial Times
Q
U
O
T
A
S
More clues leading to the result QUOTAS
Buddy explains!

The straight part
We know that "shares" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shares = quotas.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 QUOTAS mean?
QUOTAS noun- A proportional part or share; the share or proportion assigned to each in a division.
- A prescribed number or percentage that may serve as, for example, a maximum, a minimum, or a goal.
- A restriction on the import of something to a specific quantity.