The campaign, known as V-2015, is careful not to support a specific party, but is working to ensure Netanyahu does not win Israel's March election. Because the effort is not supporting any specific candidate or party, Dr. Lerner said, foreign funds -- meaning monies coming from outside Israel -- raised by the campaign are not subject to that country's campaign finance laws.
Apparently, there are things that are illegal -- supporting a particular party or candidate. Working against someone, by this paragraph, appears to be within the allowed limits.
I'm betting there are even restrictions on that, but without an Israeli campaign law in front of us, it's hard to tell.