Depends on your instance’s definition. We define it as:

3.6. Vote Manipulation: Attempts to manipulate the voting system is not tolerated including the usage of sock puppet accounts, target voting someone for who they are rather than their content, and mass downvoting posts.

We once banned a few accounts for mass down voting, i.e. their (total downvotes - total upvotes) were over 6 000. One account had downvoted more than 10 000 times in a single community.