In a share buyback, the company buys its own share for example in the open market.
The bought shares can be retired or kept as treasury stock (reference).
One such operation was carried out by Unicredit.
In the shareholder's meeting, some shareholders voted against the cancellation of treasury shares with no reduction of share capital.
Notice, not the share buyback, just the cancellation of the shares already bought.
See shareholder's meeting notes at page 156.
Why existing shareholders, who either will or will not sell their shares, should be against the cancellation of wanna be treasury shares?
What they have to lose if the company retires its own shares?