These companies invest specifically so they can get stuff on the ballot at shareholder meetings and it often doesn't take very much at all. I believe it depends in part on the bylaws of a given corporation.

There's a similar group with a similar agenda who trolled GE after GE announced some kind of wind power initiative. I don't know how much stock they owned but given GE's market cap at the time, I'm sure it wasn't a lot of the company on a percentage basis...