It may be a form of vandalism, but it's not against the rules. This has happened with a few proposals in the past. For more information, see this MSO post:
The same thing has happened a few times on the Arduino proposal.
Moderator investigation was requested and carried out, this was the
response:
I looked at the actual voting data on the example questions and there is one person who cast a large number of downvotes. It looks
like there's a user who doesn't think the proposal should go through
or that the proposed questions belong to it, which is entirely fair.
This is exactly what Area 51 is for.
The way the system is designed, it's impossible for one person to bring down an otherwise viable proposal. So, while you are right and
someone is downvoting a bunch of questions, I still wouldn't worry
about it. Presumably your proposal will have more supporters to offset
this. :)
While this is a lousy way to express your disagreement with a
proposal, it is not illegal